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MG MGB Technical - Sputtering under load
| 73 BGT, HIFs. Was running great when I got it out of the garage for the spring run. Now it is sputtering under load. Connected a dwell meter and the idle rpm is good and stable, and the dwell is about 57-60. Carbs have oil and are balanced.
I did notice a little jitter on the tac when sputtering. Confused because it seems to be running smooth at idle while checking dwell and carbs. Problem seems to have started after a fuel fill up. I must be overlooking something. Will check the plugs as soon as it cools down from the run. Thanks for any ideas. Pat |
| Patrick Callan |
| Tach fluctuating with the misfire usually indicates an ignition problem as other causes would usually only slow the momentum of the car and engine gradually.
With an LT problem usually the fluctuations are very noticeable, but 'a little jitter' sounds much less than that. I have head that HT problems can have a slight effect on tach reading but not experienced it. If opening the throttle sharply, or occurring under load causes it as seems to be the case, that is another pointer to HT. Check inside the cap is dry (and that the heater valve isn't leaking) and that there are no signs of tracking (although a V8 cap that was breaking down didn't have any signs). If you can reproduce something like it opening the throttle sharply then shut the car in a dark garage with the bonnet up and look for sparks round the HT components. |
| paulh4 |
| Plugs look clean, plug wires show no signs of breakage or wear. Distr cap looks good and dry.
Nice clean plugs and smooth idling while I had test equipment connected has me a bit confused. The "jitter" that I saw may have just been a minor fall off of rpm on misfire/spit. Weather here lousy today, so I will probably wait until I can get the car outside. I have a spare coil and condenser, so might try those (maybe try a second condenser on a pigtail). Since the plugs looked so clean, I don't know if those are even candidate issues. Will update if I get any results. |
| Patrick Callan |
| Original coils with riveted terminals can come loose, they were replaced by studs and nuts during production.
Condensers usually work or they don't - and if it's a new condenser then it's a case of usually don't! Any ignition components are best obtained from Distributor Doctor, not even the usual MG suppliers let alone eBay. A second one connected externally between the coil-ve and earth won't do any harm. Old plugs can cause hot starting problems, or break down under load i.e. wide throttle opening. Where those old plugs come from in those pictures of example of bad plugs I don't know, I did 25k on a set and they were nothing like any of those, but did cause hot starting problems. That was an error, I'd been having to change them every few weeks when the V8 wouldn't cold start and I needed to be somewhere so didn't have time to diagnose. When I finally did it was the cap, and I just forgot about routine replacement of the plugs after that. |
| paulh4 |
| The heat (and heat cycles), vibration and movement of the car going along can effect ignition electrics (wires, connections) and be unseen.
I'm not a big fan of DIY test equipment and of course professional equipment can need checking/testing and calibration. I've obviously no idea if there's anything wrong with your cap but visual checks even with a magnifying glass can miss bits - I like simple, easy and free tests like Paul suggested of looking for sparks in the dark, we used to spray mist water around to encourage light displays. Looking at plugs i'm not sure tells you a lot, unless you switch off ignition with going along and then immediately check them as a good drive or revving up can blow them clean. Points are always a PITA I don't give them car room but condensers are usually very reliable (unlike modern made CB points) and long lasting. Modern made rotor arms often through up intermittent and hard to track down faults. Test one thing at a time, if you have any other reliable HT leads you could trying swapping them (as a set to save time) as owners hold on to items like HT leads (and plugs, caps) long after they've passed their best and seeing and finding fault on them can be difficult without full pro diagnostic machines. Checking all wires, HT and LT, and connections visually and with wiggle test (with suitable care) without and with the engine running (with lots of suitable care) can sometimes turn up the unexpected. |
| Nigel Atkins |
| "Problem seems to have started after a fuel fill up". Fuel at the station can be contaminated, usually with water. Run this tank down and fill up from another fuel station. |
| Allan Reeling |
| ETA: Paul posted whilst I was still typing - and I missed the bit about problem seems to have started after a fuel fill up. |
| Nigel Atkins |
| I take it you have checked that the fuel filter isn't waxed up which may have been a result of the car standing unused for a time? Fresh petrol may have pushed crud along the fuel lines. I experienced the same symptoms as you some years ago - changed the filter & problem went away.i experienced similar problems when the carb valves were sticking. Again, removed dashpot & carb tops,cleaned valves & smooth running again under load. Cheers, Charles |
| Charles9 |
| I'm leaning toward Allan's view that it could be fuel, specially if it's only since you filled up
Most fuel now has a bit of ethanol in it which makes water in the fuel harder to diagnose Years ago the water would mostly stay seperate to the fuel and easy to find but now with the ethanol in there, the water mixes with the ethanol and the result is slightly milky fuel but hard to pick up on that as it goes through filters ok and is basically just a pain If you get some of your fuel out of the car and splash it on your w/shop floor, if it's ok it will evaporate off clean but if it has water in it or the fuel is dodgey it only dries off slowly and leaves the cement floor a bit slimey for a while willy |
| William Revit |
| According to Moss and the American EPA ethanol-laced fuel at 10% absorbs 50 times more water than non-ethanol fuels. Separation into liquid water can occur, but is less likely with oxygenated fuels than otherwise. The EPA document goes on to say "Water in solution operates as no more than an inert diluent in the combustion process. Since water is a natural product of combustion, any water in solution is removed with the product water in the exhaust system. The only effect water in solution with gasoline can have on an engine is decreased fuel economy. For example, assuming a high water concentration of 0.5 volume percent, one would see a 0.5 percent decrease in fuel economy. This fuel economy decrease is too low for an engine operator to notice"
Could still be contaminated fuel from other causes of course, especially if the effect on the tach is only one of reducing engine rpm and not erratic trigger pulses. |
| paulh4 |
| In the real world if the fuel has sucked up moisture and gone milky it will be harder to start cold and won't take the throttle at all well |
| William Revit |
| All the more reason to get the engine warmed properly and give the car a sustained and long blow-out run (Italian tune-up) - subject to the car being in good condition it should get progressively better running on the ride do the rest of the car and driver good too. At the moment, imagine being able to drive the car . . . |
| Nigel Atkins |
| "All the more reason to get the engine warmed properly and give the car a sustained and long blow-out run (Italian tune-up)" Not easy when it won't start ... |
| paulh4 |
| I thought it did start now, so it might next and when it does it should be given as I put before then perhaps it might start from then on. If not at least there was a good run out.
You must have some reward for farting about with these cars and to me it's not static, cosmetic, mechanical / engineering fiddling about. And I do mean driving not sleepy passengering behind the steering wheel. I'm an animal I don't like Tartan red, chrome wire wheels (or wire wheels really) and generally bling bits. But each to their own, it takes all sorts, it'd be a boring world if we were all the same. |
| Nigel Atkins |
| Over the weekend, I found a loose wire on the negative side of the coil. It actually came off when I touched it. So, today's goal is to repair that connection, try again, and see if the issue continues. |
| Patrick Callan |
| Sorry, make that the positive side of the coil. |
| Patrick Callan |
| That wasn't it. Very disappointing.
Distributor looks great - clean and no streaks or cracks inside. All plug wires tight. Starts ok (although) ignition light stays on longer than I remember. Once warm it idles ok, but when accelerator depressed, there is a random noticable down-tick on the tach accompanied with a small spit. Have not tried the older coil that I found in my toolbox, but that seems to have a resistance out of typical ranges. Next step is to remove the current coil and check resistances on that unit. I did find one plug with minor discoloring on the center ceramic that surrounds the center electrode, but did not see any cracks or streaks. Guess I could try a new plug there. Thinking small steps one at a time until there is a difference. Might also get some dry-gas, as it will take a while to use up the last tank fill. |
| Patrick Callan |
| Checking all wires and connections are all clean, secure and protected is always worthwhile, bearing in mind breaks or poor connections can be hidden from sight.
Does the dissy need lubricating as required, grease and oil. Replacing one plug to find the fault is fine but they're so cheap it's then best to replace the whole set with new (rather than ones literally knocking about on the bottom of a tool box). How's the rotor, black rivet job perhaps arching out? I don't know these complicated USA cars, could one of the added electrical devices, or rev counter or o/d switching cause something like this. I always favour starting a service check from tappets on (if not done recently) as that follows a logical path to start with to check and adjust as required and your looking what's to and around these items. Then move on to a more diagnostic flowchart style. Particularly suspect any modern made new parts you've fitted in the last x numbers of years (depends on car's useage and mileage over those years). |
| Nigel Atkins |
| When you open the throttle vacuum advance changes and twists the points plate. If you have points (or under-cap electronic ignition) the coil is earthing through the points and a cloth-insulated wire earth between the points plate and the distributor body. That wire is continually being moved back and fore and can fray, giving an intermittent connection as throttle position changes.
Similarly the points wire, which is also cloth insulated on a 25D4 between the points and the spade on the side of the body. 45D4 distributors have the points wire exiting the distributor body via a hole in the side, that is plastic insulated, more flexible than normal wire, but the conductors can fracture internally. |
| paulh4 |
| Current Coil info: primary = 6 ohms secondary = 6 Kohms I have an old coil with the following info: primary = 6 ohms secondary = 11 Kohms Not sure why the newer coil has a secondary reading so much lower than the older coil, but it has been running well until very recently. The 6 ohm reading on both coils seems a little high compared to stats that I have found on the internet. |
| Patrick Callan |
| I had a similar problem recently with my MGA, it developed an intermittent misfire that made the both electronic rev counter and the fuel gauge needles dance around.
I began to search for a bad connection on the ignition circuit, I actually replaced some sections of the ignition wires under the dash. Then I remembered a similar fault that had happened 8 or 9 years earlier, I took out the main fuse that supplies the ignition circuit, gave the fuse holder a clean up with fine emery cloth and fitted a new fuse. This solved the problem. I suppose 60 year old fuse holders need a bit of care and attention every now and then😀. Hope you problem is as simple, Colyn |
| Colyn Firth |
| Good point, checking electric connections starts at the battery post/clamp/lead and goes forward from there including, bullets, spades and switches - and the often forgotten fusebox and fuses. Pat, have tested (checked/confirmed/calibrated) the tester (testing equipment for coil). I've found cheap modern digital stuff last about 12 months (1 month after warranty ends) and they don't like to be stored in the cold. |
| Nigel Atkins |
| Thanks to all for some great info. Rainy day here again, so I guess it will be a good time to spend rechecking connections and hoses. Still a little baffled by all the info available on coil resistances. Is the 3 ohm value a "minimum" or a "maximum" value? |
| Patrick Callan |
| 6 ohms is way too high - unless they are for a 24v system! As you are getting that on two coils I'd tend to suspect the meter you are using. The book quotes 3.1 to 3.5 ohms, but sport coils are usually around 2.5 ohms. Secondary resistances can vary significantly from coil to coil, 5.4k for a standard 12v coil to 8.9k for a high output 6v coil, so whilst your 6k could be in spec the 11k again seems high. |
| paulh4 |
| I'd suspect the coil. I once had the symptoms you describe on a Mini. As Paul H says, my Lucas coil measured 3.5 Ohms. I checked it before fitting Luminition. |
| Paul Hollingworth |
| Test the testing tool before carrying out every individual test.
If the instrument is faulty/unreliable/erratic/intermittent then you could get any correct or incorrect reading at any time and in any sequence. I recently used a simple continuity test and it worked on testing the instrument itself before testing the item then gave a negative result on the item, and then failed to work on testing the instrument itself after but gave a positive result on the item immediately after that. So without the testing of the instrument itself after the item test there would have been a false negative to the item test. This was from a cheap modern digital multimeter that started playing up after a couple of years, the previous same cheap model played up after 13 months (not 12 as I put before) one month out of guarantee. Both cheap multimeters were brought for me as presents by two different people. I normally use a very cheap simple analogue continuity device but I wanted to teach someone about testing and the unreliability of these cheap digital multimeters and that if you believe them without question you'll have 'fun' with wiring and diagnostics. Something to bear in mind with the Donald's dozens of different tests that'll be available. |
| Nigel Atkins |
| Update: My bad on the meter readings. I was not zeroing the meter for each reading. The old coil (still not hooked up) reads 8 Kohms on secondary, and 3.2 on primary. I suspect my lack of attention on the coil that is back in place would result in similar numbers, but I will remove it and check again with proper zeroing of the meter. Sooooo, if that holds true, the coil does not appear to be the culprit. Back to checking connections and hoses. Thanks for the continued advice. |
| Patrick Callan |
| Yup, coil in the car seems good: 3.2 ohm on primary 6 Kohm on secondary. |
| Patrick Callan |
| Most probably still dodgey fuel if it only happened after you refilled There didn't happen to be a tanker at the servo refilling the tanks at the time,-? That's a fantastic time to pick up a load of rubbish |
| William Revit |
| The coil seems good with a cols static test, but can be breaking down when it gets hot when running.
I've diagnosed problems like this by connecting a voltmeter positioned in the cabin where I can see it, connected to various places. In this case the coil +ve and -ve would be the places to test for and ignition LT problem, and an analogue meter will probably give a clearer picture than a digital. If you find the voltmeter jitters downwards with the sputtering when it is connected to the coil +ve then the problem is the 12v supply to the coil. If it jitters upwards on the coil -ve then it it is the circuit through the distributor that is failing. If it jitters downwards it could be the coil or the circuit through the distributor, there are ways of determining which. |
| paulh4 |
| Ah, Patrick, you were the testing tool in this instance and very start of the process - test the tester (person). :) But good on you, you admitted your mistake, many wouldn't and some even couldn't. We've all done something like it, most electricians I've dealt with would tell you until they were blue in the face they'd checked and the instrument needs checking or of course back "in the old days" blame the apprentice who'd have to accept the blame, and the cycle begins. |
| Nigel Atkins |
| Thanks again to all for continuing to follow this thread. Finally have some sun this AM, and did some contact cleaning yesterday (including fuse block), so hope to try again today. Could not find any breaks in vacuum lines. Will continue to follow small steps, and eventually use up the current tank of fuel. Have to see if I can identify an easy place to connect my volt meter. The station where I filled up is usually reliable, but who knows.. Will post more if anything changes. |
| Patrick Callan |
| No real progress today. After cleaning contacts and rechecking vacuum lines, I still get a quick down-tick on the tac when I step on the gas. Also keeps making down-ticks if I hold the rpms up.
Another symptom appeared today - don't know if it is related. When I turn the ignition off, it takes significantly longer for the oil gauge to drop and for the anti-runoff valve to click (even though it is not running on). I don't know of anything that I touched that would have impacted that. I did check the valve, and that works on a static check. Just for grins and giggles, I switched coils, and the same thing happens. I guess fuel could still be an issue, but if that were the problem, I would expect the down-ticks to happen at idle as well. Soooo, back on the hunt. |
| Patrick Callan |
| The anti-runon valve only clicks when oil pressure has died away (which you may already know). As to why the oil pressure is taking longer to die away, that depends very much on oil temperature i.e. how long you have been running the engine. In my experience fresh oil also takes longer compared to 'old' oil, but not for very long. Nothing to do with the sputtering and tach ticks, that I can imagine. |
| paulh4 |
| Found a nearly broken wire on the + side of the coil. Checked my wiring diagram, but the one for a 72-74 did not show that wire from the coil. Looked at the diagram for the 75, and it was there. So, I guess my car is a bit of a mutant between 73 and 75. Probably a few "mods" from a PO as well.
Anyway, tried disconnecting that wire to match the 73 diagram, and the car would not start. Reconnected it and the car starts, but back to down-ticks on the tac. The 75 diagram shows that wire to go to the instruments, so I am not sure why it would prevent starting, but maybe it leads to a ground somewhere. Going to be tough to trace this if the car is an "in-betweener" for wiring. Rechecked the oil pressure, and as Paul stated, the anti-runon valves clicks when the pressure goes to zero. And it goes back down slower for a cold engine. I guess it is back to wire connection tracing, especially since I have found a couple questionable connections. |
| Patrick Callan |
| I've been trying to help a midget owner with a car with molested wiring and possibly wiring from the next year or more likely a mix because of PO interferences.
I don't know if the Haynes or Bentley wiring diagrams are spot on accurate or even those in the factory workshop manual but be aware there could be errors and some diagrams can include options or alternatives for a range of years that aren't applicable to your car. I always prefer the diagram in the relevant Driver's Handbook especially if it's a period original rather than modern reprint (I scan and enlarge it for my eyes). The factory workshop manual and colour wiring diagrams are available in pdf format on the internet. Your car number G*** should give you an idea of build date for wiring but nothing is in tablets of stone. Check the diagrams against reference points on the car, wires from fuses, loom, switches, loom plugs and the colour and positions (switch contact numbers fusebox numbers,ect.) to see if you can establish which wiring year you have. |
| Nigel Atkins |
| Looked at the manual in the car, and that didn't seem to match the wiring either, so I went to the web. PDF files from the Bentley manual for 72/73 look much closer to the wiring near my coil and distributor. Gives me a few other connections to check - especially those to the tac and fusebox. More checking in store. |
| Patrick Callan |
| Pat, be careful with just taking one point of reference, the wiring and/or the associated parts might not be as factory original, better to also check two or more other points. Did you get the 'advance Auto-Wire' set in colour that covers both Bentley and Haynes wiring diagrams, if not here they are. - http://www.advanceautowire.com/mgb.pdf |
| Nigel Atkins |
| Is it a chrome bumper or a rubber? A 73 would be chrome, a 75 rubber. The change was half way through the 74 model year hence the first rubber bumpers are known as '74 1/2'.
The most obvious difference between CB and RB is that the former have 12v ignition whereas the latter have ballasted ignition with a 6v coil. The former has a single white on the coil +ve and the latter two white/light-greens. Both have two white/blacks on the coil -ve, one from the points and the other to the tach. This was all as they came out of the factory of course, it could be anything now. The tach and fusebox connections were the same on both, the last time the tach wiring changed was for the 1973 year and the fusebox wiring didn't change until the 77 model year. But the chassis number will tell you closer than anything exactly what it is (was!). North America had additional plates on the drivers door pillar and at the base of the windscreen, I'm sure I've read that the date stamped on the former wasn't always correct, sometimes quoting the following model year number. |
| paulh4 |
| I know it's generally accepted that tachometer Ticks, or whatever, are usually associated with low tension issues, and that's worth pursuing that. A photo of the coil and fuse box area would help us. I'm not entirely sure about the anti run-on valve and where it is sited. Assuming it dumps air into the inlet manifold, could it be leaking air when non-active? |
| Allan Reeling |
| The anti-runon valve is open normally, and only closes when you turn the ignition off, then when oil pressure has dies away it open again. It works by closing off the fresh air source for the crankcase ventilation to the charcoal canister, which causes the ventilation vacuum in the canister to increase. And as the carb overflow ports are connected to the canister, the increased vacuum sucks the fuel out of the jets so stopping the engine.
It was a year or more before anyone realised that was, in fact, the ONLY thing that was stopping the engine once the ignition relay was provided for the 1977 model year. For reasons I won't go in to the relay was remaining operated when the key was turned off, and the relay was powering everything (bar the ignition warning light ... clue). It was never a problem on UK cars as with no anti-runon system they discovered the problem straight away, but only corrected it on those cars by changing the wiring round the relay. It was only when owners of LHD cars started complaining they couldn't turn the engine off - because of a defect anywhere in the emissions system - that they made similar changes. |
| paulh4 |
| There's an additional problem when referring to the year of the car that of the marketing 'model' that is the year in advance of the build year. Another reason to look for the car numbers. But of course any information relating to those numbers about strictly was was used in the factory build may be inaccurate but it's a good starting point at least. I think good clear photos can help a lot, especially if in the correct orientation, and now there can be two per post. |
| Nigel Atkins |
| Thanks all, lots of new info to process today.
I didn't get the wiring diagrams from that source, but I just checked, and the ones that I downloaded are identical to those. Chrome bumper, single white on the coil +ve, two white/blacks on the coil -ve, one from the points and the other to the tach. A couple of the connections were loose, but that could have been from me checking everything multiple times, and even removing the coil a couple of times. Have tried to ensure all tight now. Not sure about the anti run-on leaking air, but all the hoses look fine, and the sudden onset of this problem seems to rule that out. I downloaded several wiring diagrams, and will look closer at them today, but the coil connections seem to be consistent with the diagrams. Wire colors are tricky due to PO adding pigtail to wires when replacing end connectors, but I think I have that all straight, and it was running great before this started. Beginning to wonder if the coil might still be the problem, even if static readings are correct. The older one reads correct too, but I must have replaced it for a reason. |
| Patrick Callan |
| Have you got access to a known good functioning coil of the correct type you could borrow to try it.
Or just buy a new coil and if that was the problem throw/recycle the previous one, if it wasn't the previous coil at fault then you have another spare for your collection. I know this involves monetary and other associated costs but you want the correct ratio of car running well and reliably so you can drive it and more often to fiddling about on it and with it. Unlike many on here I loathe doing anything on my car other than driving it, I only do the servicing, maintenance and repairs as I can no longer afford to pay sometimes idiots to do the work and sometimes shodderly, so I have an idiot very reluctantly work on it but at least I don't have to pay myself money but insist on a fair driving to working on it ratio. |
| Nigel Atkins |
| Ordered a new coil today. Not expensive, so it seemed like the next small step. Should take a few days to arrive, so I may not have anything new to add for a while. |
| Patrick Callan |
| I've replaced a coil before just because it was so cheap to do and life and time go by so quickly I wanted to cut down on wasting both on a car.
They were (still are?) about £13 but I paid about £18 for a sports coil to go with other changes previously made. Like HT leads coils are difficult to measure for all faults unless you have professional diagnostic equipment, £10-£30 for the lead set but £50-60+ to go on the testing equipment. I used to normally change things like HT lead set (dissy cap, rotor arm - throw out points and condenser for electronic) soon after I got the car and as service items at certain intervals. To cut a long story short I didn't get round to it on a V8 and it suddenly cut out but immediately restarted, done it a second time so as it had (factory fitted) electronics and an ECU I took it to a tuner - and he found it was one HT lead causing it, dancing the spark in the dissy cap IIRC. If only I'd got round to replacing the HT lead set that looked fine but I didn't know the age or use and abuse of. |
| Nigel Atkins |
| The voltage tests mentioned a few days ago should tell you if the coil is playing up, and help you localise it even if the coil is not the issue.
Have you examined that distributor earth wire yet? With a new coil measure the resistance to check you have been sent a 12v coil i.e. 3 ohms primary! I've learned from others not to replace stuff as a routine especially ignition components. although latterly sources like Distributor Doctor are better than the usual suspects and especially eBay. Still don't replace them until needed though. I put a set of silicone HT leads on the V8 when I got it 24 years ago as those it came with were mixed. As part of a thread somewhere I did check the resistances a couple of years ago and found the coil lead (the shortest by far) significantly higher than even the longest to replaced it. It didn't make any difference to anything, so I suspect it had been like it all along. That's another thing I would check on receipt rather than simply fit, same with a condenser, but I've never had points or a condenser fail in over 50 years. |
| paulh4 |
| Paul bench testing isn't the same as real world use. Just because something is working or working within tolerance doesn't mean it's working well and is not passed its optimum and in decline, not working as well as it could or perhaps should.
The level of performance a classic car owner is willing to accept or generally use with their classic is up to them, the more performance, which includes mpg, reliability as well as power and handling the nearer the components and parts have to be to good function. I prefer to change parts with good quality new parts in a timely manner before they get too tired to noticeably affect performance (and you don't generally notice steady decline much) and definitely before they play up or fail and have me at roadside stoppage (I've had enough of that with various classics to last me two lifetimes). Normally I'd say coils seem to last decades so don't change them - but if they seem to be play up regardless of any amount of bench testing and being within expected readings for the small cost of money over farting about on the car I'd replace, and have. It seems original condensers also last many decades so I wouldn't change those as a service item and I'd be very, very careful about where I bought a replacement from, most newly made ones are crap. Going back very many years new made CB points have often been crap, if you have very old ones or old NOS then they could well be long lasting and not need so much farting about with. I and very, very many others have had problems with CB points but in hundreds of thousands of miles in various classics as daily use cars I've never had any problems with the various replacement (and upgrade) electronic ignition systems I've had and they have been better performance in all areas over the CB points and condenser. I do agree with you though about thoroughly checking the dissy earth wire, even a thorough visual check can miss a problem on it. |
| Nigel Atkins |
| Patrick
I'm still leaning towards grotty fuel causing your stuttering but the tacho flickering won't be caused by that One thing that could be the issue is if the little carbon post inside the dist. cap that runs on the rotor button, - If that's missing or the springs jammed it will cause a little stutter and depending where the spark jumps to could play tricks on the tacho With the meter hooked up does the dwell flick at the same time as the tacho, if it does it could be just the ign points need cleaning up willy |
| William Revit |
| I haven't given up on the issue of nasty fuel, but it will take a while to drain the tank. Meanwhile, checking as any small things as I can find. When I had the meter attached, the car was idling, so I did not notice any jitter in the dwell (or sputtering, for that matter). The distributor looks very healthy - inside and out. Could potentially be the vacuum line between the manifold and the distributor, but I believe that impacts idle rather than under load.
Staying frustrated, but still at it. Nice day today - would love to be driving. |
| Patrick Callan |
| Patrick,
I am not sure from reading all the various posts whether you have checked & double checked the spark plug gaps. Two or three years ago i had a problem that every time i drove the car at higher speeds then the engine would splutter , but would run smoothly when i eased off. Having checked the plug gaps i tried a different distributor cap & rotor arm ,coil, fuel delivery rate & fuel filter.(I do run the car with a 123 electronic distributor that has been faultless in the 10 (?)years i have had it). The problem still occurred - i got a neighbour to check the plug gaps & to my embarrassment he found one to have an excessive gap! This was adjusted & thereafter the splutter disappeared. Worth checking again? Cheers,Charles |
| Charles9 |
| Plug gaps are a easy, quick and virtually no cost check to make. It'd be included in the overall service check I favour, from tappets on (if not done recently) as it follows a logical path to start checking on (and adjusting as required) and your looking at what's to and around the service items so could spot problems. |
| Nigel Atkins |
| A mate has a sportscar that had a very intermittent but bad backfire. I suggested he removed the chip that had been fitted, fully service the car and set it back to factory and see how it went before putting the chip back on and re-adjusting.
He didn't want to remove the chip and only had a basic service (engine oil & filter change and a few checks). The backfire continued. I suggested a proper service (of the whole car) or at least trying changing the spark plugs, a £10-11 cost, as they been in the car a good while and his Driver's Handbook had to change 12k-miles/12-months. He didn't change the plugs as the factory Workshop Manual had change at 12k-miles/12 months for performance (this is a performance car!) but they could be changed at 30k-miles, despite having the car a number of years the plugs hadn't done 30k-miles since the previous owner changed them. I explained the 30k-miles did assume the plugs were without fault(s). Eventually he changed the plugs, £12, and the backfire virtually went away - but a few years of backfire had been going on already. He's possibly caused hundreds of pounds of engine damage and work by not changing the plugs. But the car still ran and continued to run (reasonably?) well with only a slight occasional misfire. This took place over a number of years, today I heard he's got problems with the car, I don't know what, I wonder if it's just flickering lights or something like that(?). |
| Nigel Atkins |
| Nigel, this is a new coil. It seems eminently sensible to me test it to confirm you have been sent the correct one and it passes static tests. YMMV. What it does on the road is another matter entirely.
You may choose to keep paying someone to fit new parts until the problem goes away, I prefer to diagnose to determine the cause of a problem, then fix it. Especially with electrics the problem could be in any number of places and swapping parts disturbs other things nearby and may cause the problem to disappear. For a while. If the cap contact is missing or faulty it will probably show burning or arcing as on the attached.  |
| paulh4 |
| Plug gaps are perfect. Hooked up a condenser on a pigtail. No change. Rotor and points all look perfect. Next step is to wait for a new coil to arrive. |
| Patrick Callan |
| Paul, as Pat has put the new coil is yet to arrive so can't be tested.
Yes I too like to resolve the problem, but without the need to have or buy lots of testing equipment when lots can be sorted with wires, connectors and a bulb, but they wouldn't cover the coil or HT leads. Somethings aren't worth the cost of finding out, I've not suggested changing parts willy-nilly but if it gets the car working reliably and at better performance and you can afford the new parts why not. The point of the car is to drive it for some of us not farting about with it - but as always each to their own and whatever floats your boat. I replace service parts at the start of ownership so I know exactly what is fitted and when and that it (should) be fully working to very good performance and condition and reliable. I've enough experience now to generally know which modern parts are piss-poorly made and/or crap, which is too many. It all depends on if you want to drive the car in a spirited way or accept that it goes reasonably well for pootling along steadily. You could have some 10, 15, 20 year old tyres (and many do) with loads of tread left, no damage to sidewalls and you can pootle along with as long as you take it steady (I wouldn't have them) and it doesn't get too damp on the roads (and don't need to emergency stop) but if you want to be safe and have the car braking, handling and holding in more comfort for more spirited driving, you'd get a set of new tyres. But why get new tyres when the old ones still have plenty of tread and aren't damaged, hold on to them (is one attitude but not mine). |
| Nigel Atkins |
| Patrick
The word perfect appears in your description of things a bit Have you had the ign. points out and inspected them or are they perfect just looking in there Is the carbon button in the cap good and free to move When you had your extra condenser hooked up was the old one still hooked in there as well, if so your test did ------------nothing Next-rotor buttons- they can 'look' perfect and be dead----To test it, remove the coil lead from the cap, remove the cap from the dist, then using a well insulated holding device hold the end of the coil lead about 1/8"-1/4" away from the centre of the rotor where the carbon button runs--Then get your assistant to spin the engine over on the key for a max of 3-4 seconds--If a spark jumps to the rotor in this time it's faulty, no spark,all good Don't spin it over for more than a few secs otherwise you can kill the coil willy |
| William Revit |
| Willy,
For me, perfect = on spec. Distr cap carb button good, inside cap shows no cracks or tracks, points clean and gap set to spec, wires all in place, no cracks or loose ends. When at idle, dwell and rpm looks correct and smooth. Prior to this problem, running had been smooth with no spits or tac jitter. Using the pigtail condenser was kind of a shot in the dark - they are supposed to work if the one inside the distr cap fails (even if it is left in place), from what I understand from other posts and internet searches. However, it may be ineffective for a condenser that is intermittent. Figured a try couldn't hurt. Made no difference, so either the currently installed condenser is fine, or the trial doesn't work for intermittent condition. Your spark test scares me a bit, so I think I will wait for my new coil to arrive before I try that one. Coils are relatively cheap, so if that doesn't do anything, having a spare isn't a bad idea. Pat |
| Patrick Callan |
| Pat, is the dissy greased and oiled as required (occasional or at a service) keeping the points free moving and the dissy and its advance moving freely. |
| Nigel Atkins |
| Nigel, Yes, lubed per manual. |
| Patrick Callan |
| Should be good then, well as good as they are, well done. |
| Nigel Atkins |
| Two condensers in parallel?? If one is breaking down (i.e., creating a dead short to earth) having another in parallel will do nothing. The little electrons will take the easiest path to earth through the condenser that is breaking down. My experience, albeit just a bit more than 10 years, is that condensers fail to short, not to open. If the failure is to open then the second one in parallel will save the day but that's hard to detect. Test it again with a known good condenser by itself with the suspect old one removed. The condenser can be mounted outside of the dizzy for ease of changing as long as the tab has a good contact to earth.
Jud |
| J K Chapin |
| Putting a second condenser in parallel with the existing is a valid test of the existing condenser. If the problem remains then the condenser isn't the problem. If the problem goes then it probably is.
But condensers rarely go intermittent, generally they either work or they don't, and replacements from many sources these days are highly suspect and can fail within a matter of hours. I've never had one fail in over 50 years, I don't routinely replace things like that, the one in my V8 came with the car 25 years and 120k ago and looked 'old' then. |
| paulh4 |
| Forgot to add: Also checked battery connections and engine ground strap connection. All good. Waiting for replacement coil. |
| Patrick Callan |
| Good one Pat, but any other live or earth connections, big or small, can cause issues, all need to be clean, secure and protected. I'm so keen on the arrival of your coil I think when it arrives I'm going to name it! |
| Nigel Atkins |
| Battery cables and engine earth strap will affect cranking, but rarely running as by that time the alternator is providing the power anyway. Certainly no harm in checking, but the only valid way is measuring the volt-drop when cranking, as per the Lucas Fault Diagnosis Manual. Did you check the distributor earth wire yet? And if a 25D4 the similar wire from the spade connector to the points? |
| paulh4 |
| Paul, yes - have checked both of those wires. I have been checking and re-checking all ignition related wires and connections. Have found a couple loose wire connectors, but tightening them has not made any difference (so far). |
| Patrick Callan |
| I was thinking of all wiring and connections in general on the car not just relating to this current issue, If you check something and make the lights brighter you're still gaining. And it's something to do, and usually very worthwhile, whilst waiting for the arrival of the coil. Expected dates are no good, could come early or late, need things to keep your mind off it until then. |
| Nigel Atkins |
| Still got my money on the fuel but the tacho flick is interesting--
Have you measured the resistance of each plug lead and coil lead from inside the cap to the outer end of each lead, if not do that and give them a good wriggle round while measuring--have you checked in the posts of the cap for corrosion , measure the leads first but then pull them out of the cap to inspect each one and clean as required Which rotor button are you using- colour, rivited or moulded A more detailed description of sputtering would be helpfull Also , Jud is correct in what he and I have both mentioned ,If the condenser in the dist is breaking down to earth it will still do it no matter how many new ones you connect on the outside , the condenser inside has to be disconnected out of the circuit to eliminate it from being a causal part Condensers do funny things at times-causing all sorts of running issues |
| William Revit |
| Well, maybe some progress (I hope).
While waiting for the new coil to arrive, I checked the resistance on all the plug and coil leads. All measured identical with analog meter. Rotor is a red one from Jeff S. Coil arrived mid process, so I installed it and re-checked coil connections. Started and ran through a range of rpms - no spit or tac down-tic. Hope that means something good. Now have to wait for a decent weather day to take a drive. I will update after a good drive, and maybe a fuel fill up (with dry gas), but thanks to all the info you have all provided. |
| Patrick Callan |
| Pat, the coil has arrived, great. And it's good news, so far at least, let us know how you get on with real world road testing. Obviously I now have a vested interest in it being the coil that was at fault despite bench test readings. I had to look back to see who first suggested coil, good on them, a quick look and I think it was Paul Hollingworth, good call Paul if so. So ... how much did the coil weight and what's going to be the name. |
| Nigel Atkins |
| Did you check the coil resistances? |
| paulh4 |
| New coil resistances on spec, but then the old one was as well on a static test. Can a coil go bad internally and still look good on resistance check? Weather terrible here today, so an underway test will have to wait. |
| Patrick Callan |
| Anything is possible. It's why having a voltmeter connected to various places in the ignition circuit when you can reproduce the problem can be helpful in determining where the problem lies.
I trust you haven't binned the previous coil? While it is raining you could re-fit that and see if you get the problem when blipping the throttle as before. If so then it looks like the problem is with the coil. Personally I'd then do the voltage tests but I'm anal about things like that. But if you don't get the problem with the old coil then it could have been disturbed while changing it, only to come back again at some point in the future. |
| paulh4 |
| Paul,
I am getting paranoid in my old age, so after I responded to your previous post, you got me questioning my readings and memory of the values on the old coil. So I measured both the old and new with my analog meter (made sure to zero prior to each reading this time), and here are the numbers: New coil: 2.6 ohms primary, 10K ohms secondary Old coil: 3.2 ohms primary, 6K ohms secondary Older coil: 3.2 ohms primary, 8K ohms secondary The secondary on the new coil is a bit higher than the others, but my previous research has is within acceptable specs. Your are probably right about re-trying the old coil. I tried to check the running after each loose connection that I found, etc, but it is very possible that the "correction" may be due to a number of cumulative issues. Anyway,it looks like the weather may keep me inside for a couple of days. Thanks again for everyone continuing to follow this thread! |
| Patrick Callan |
| All those are OK, the new one is a 'sport' coil i.e. higher output, but you are not likely to notice the difference between that and a good 'standard' coil. |
| paulh4 |
| Well, tried to go out for a drive, and if anything, the problem is getting worse. So, I guess it wasn't the coil. Yesterday in the driveway, went through a range of rpms with no spit, smooth movement on the tac. Now it is sputtering/spitting, and the tac is jumping again. Anyway, I am beat. Back to the hunt tomorrow. |
| Patrick Callan |
| Blow !
In a way if the problem is getting more consistent that could make it easier to track down. To discount bad fuel in your tank you could disconnect the fuel pump and provide a gravity supply to the carbs and have a static trial run. Thinking of which have you checked constant flow from pump and supply to carbs, filter blockage and that sort of thing, rubber breaking down unseen under braiding on supply to or between carbs. Tach could be jumping as it's doing its job recording change in revs but might be a bit free at the needle work. Hate now to ask if you have a Jeff S(?) made rotor arm (equivalent to our Distributor Doctor Red Rotor Arm (see also about modern made condensers). - http://www.distributordoctor.com/red-rotor-arms.html http://www.distributordoctor.com/distributor_condensers.htm |
| Nigel Atkins |
| Voltmeter on the coil +ve then the -ve needed, where you can see it when driving. |
| paulh4 |
| Nigel, red rotor. Not sure I am ready to go into fuel/carb issues yet. Paul, right now, I don't think I can drive it. Will first try the voltmeter while in the driveway, and recheck all my connections. |
| Patrick Callan |
| Found another wire connection issue. Old connectors are driving me crazy. Was able to drive it, but running still erratic - misfiring, and the tac is still jumping. Maybe get back to fuel issues. I did notice that the choke has little-to-no affect, but movement at the carbs looks good and even at each carb. |
| Patrick Callan |
| If you have a spare rotor arm try changing it over - nothing to loose ! I had a supposed 'good quality one' from a tuning company fail. Then onto the fuel system ! R. |
| richard b |
| Good point from Richard, a red coloured rotor or 'Red Rotor' copy might not be as good as the real ones. The red rotor copies I bought all looked fine but were as good as Bosch or Beru (brownish) rotors but were less than half the price so good enough if they don't cause faults and at least last half as long. If you've found another loose connector you'll see why check all of the car's connectors, wires and switches is worthwhile. Keep going Pat you'll get there. |
| Nigel Atkins |
| As has been said several time a fuel issue won't make the tach erratic. |
| paulh4 |
| That's if the tach is actually erratic, more so than usual, or it might just be registering the change in revs, and there could be more than one fault present.
Describing things in text on a bulletin board with different people from different backgrounds and different parts of the world can throw up differences in meanings. How many times have you wondered what I mean! Pat's original post has "a little jitter on the tac when sputtering" which doesn't sound that erratic to me - using both words in their normal everyday general use. Usually these sort of problems are electric rather than fuel side and there's been a fair amount of stressing the electric side (for the whole car from me) but from distance going on only the information available it's worth considering fuel side too. Perhaps a video of the car misbehaving showing exactly what this 'jitter' is on the tacho and the sound of spluttering may give more direction to electric side. HT leads, coil and rotor arm no matter how many bench tests they pass on DIY equipment can play up on real road use. Of course I'm miffed it wasn't the coil, apart from it confirming a bench test it also potentially means a growing collection of old parts - but mainly because it didn't sort the problem, and get the car driven more and farting about less, the ratio is still wrong. |
| Nigel Atkins |
| Patrick: If you've found a few dodgy connectors, then replace as many connectors as you can get to. Disconnect the battery first. Cheers Gary 79 MGB |
| gary hansen |
| Thought I had it (for a moment).
Checked the plugs again, and #2 was fouled, and looked like it was discolored at the base of the ceramic. So I cleaned up my spare older set of plugs and replaced all four. Car started and idled nicely in the driveway. Figured/hoped that was the problem. Started out on the road, and the misfire started again. Kept misfiring while trying to accelerate. Got home, and it idled well in the driveway. If it was fuel, I am not sure why it would be ok at idle, and not under load. Wondering if aftermarket fuel pumps can act that way. Maybe a sticking carb? |
| Patrick Callan |
| Fuel starvation IS more likely to be noticed under load than at idle because the demand is greater. You can check delivery by removing the pipe from a carb (watch out for a spurt if the ignition has been on recently), and direct it into a container. Turn on the ignition and it should deliver at least one Imperial pint per minute, and in practice double that, in a continuous series of pulses with minimal bubbling. For an SU anyway, and I'd expect an aftermarket to have to do the same. But misfiring from that cause won't affect the tach, unless it cuts out for so long that the car is slowing down and hence engine speed, but then the tach will show a slow and steady drop while the momentum of the car is still spinning the engine.
HT is more likely to break down under wider throttle openings as the increased cylinder pressure makes it harder for the spark to jump the plug gaps, so a weak link elsewhere may well break down before that happens. That _may_ have a slight effect on the tach. But until you put a voltmeter on the LT you can't eliminate that as a cause. |
| paulh4 |
| The tach excursions are quick, so if I read Paul's note correctly that should be pointing away from fuel starvation. Guess I will have to run a wire to an easily viewed location in order to check LT voltage while driving. Not sure there is an easy place inside the car to hook into the coil +ve then the -ve, but will investigate. |
| Patrick Callan |
| Have you checked the dissy cap is secure and doesn't twist (too much) on the dissy, even the if the dissy is secure in engine clamp. Often you can get away with things being slightly out or slightly faulty but another or series of items in the chain also being slightly out or slightly fault can cause issues, and as Paul has put earlier solving one may disguise issues with the others, until thy're ready to play up more. |
| Nigel Atkins |
| Any chance this could be the ignition switch? I have a replacement. Maybe should try it. |
| Patrick Callan |
| Unusually faults are the b*ggerrs to find, wires that are fine when cold but start to break when hot but of course then work when you test them because they're cooled. Here's one only I seem to have had - HT lead boots so tight that when pushing on them it actually loosened the the king lead connection on the coil but was unseen under the firmly fitted boot. I now always burp (like with a Tupperware lid) boots that are tight when fitting the leads and boots. |
| Nigel Atkins |
| Always worth checking any newly fitted parts especially if it's a modern made part from about the last 15-20? years. Also check connections and wires on switch. I'm not sure it ties in with the splutter under load though. |
| Nigel Atkins |
| And again maybe dud fuel
The ethanol is capable of soaking up a lot of moisture, enough to make it run really bad and the fuel will be milky and if it gets to a stage where the moisture content is that high that the ethanol can't soak it up then it creates a situation where the contaminated ethanol seperates from the petrol The petrol goes clear again but the water/ethanol mix goes to the bottom of the tank and your car stops --I reckon you are in the partly contaminated area where it runs reasonable but won't take any load, the exhaust would be running red hot,so be carefull---I had a friend melt the rear bumper cover on his 911, the guy following him pulled him up in the night and told him his muffler was glowing red hot and bits of bumper were falling off Caused by---contaminated fuel Is your fuel milky Have you tried spilling some on the floor to see if it evaporates away cleanly |
| William Revit |
| The voltage test on the coil +ve would point you towards the ignition switch, but if that were failing the ignition warning light would be flicking on - as it should do when turning off a running engine although in that case it will glow and dim as the engine spins down.
As a 73 you should have an RVC tach which has a connection from the coil -ve. Before that RVI tachs had a white wire feeding power to the coil +ve, and the -ve wire goes direct from coil to distributor. But to be honest it's easier to run a wire in from the engine compartment for both tests than access the back of that. |
| paulh4 |
| Haven't ruled out the fuel issue yet, but the fill up came from a station that is usually reliable, and I would think that if fuel were the issue, it would impact both idle and under load. Idle seems to be good right now (though with my luck, that could be different today). Today's mission (should I decide to accept it) is to rig the wire for a voltmeter inside the car to watch +ve and -ve while driving. |
| Patrick Callan |
| Patrick, I'm not sure from all these posts if you have looked at and/or changed the fuel filter before the fuel gets to the carbs.Is it waxed up, which has happened to me after a winter lay off & then a shake down run? I once put a new filter in the wrong way round as the direction arrows were impossible to see. It caused problems under load but not at idle. Cheers, Charles |
| Charles9 |
| C'mon Patrick this isn't good enough, I'm sure you're old enough to remember the proper version of the show before it was turned into a star-biased film franchise - "Your mission should you - choose - to accept it ...". :) https://www.youtube.com/watch?v=0TiqXFssKMY No intro music but I bet it's playing in your head. |
| Nigel Atkins |
| Patrick, my 79 developed a gross misfire a number of years back. Idled fine and ran good up to 3k rpm and misfired, backfired, and wild tach. The lead from the coil to the distributor loosened up just enough from the terminal at the coil to allow the car to rev up to 3K. I pushed the boot on the wire back far enough to be sure the lead was in contact with the terminal then slid the boot back to the coil. Check it out. Cheers Gary 79 MGB |
| gary hansen |
| Gary,
could yours have been caused by what I posted earlier, could it be I'm not alone? >>Here's one only I seem to have had - HT lead boots so tight that when pushing on them it actually loosened the the king lead connection on the coil but was unseen under the firmly fitted boot. I now always burp (like with a Tupperware lid) boots that are tight when fitting the leads and boots.<< I think mine was just a slight misfire at start - or wouldn't start, I can't remember now. I've had so many classic car problems I can't remember which problems were on which cars and most annoying how to track them down and sort them. My wife is a lot better at picking up and recognising noises than me and will say "it's on the *whatever*, you had the same thing happen before". |
| Nigel Atkins |
| Checked the ht boot, and found a path through the firewall for wires to set up a voltmeter for +ve and -ve check. Hopefully try tomorrow. |
| Patrick Callan |
| Just for kicks pull out the air filter and take a drive, I had the same symptoms on two occasions over the years in my 79 B and it was a plugged air filter. |
| L Frisch |
| Nigel, yes it is possible you mentioned the coil lead wire. Perhaps I missed it. L Frisch, I think a clogged air filter would make the car run rich making plugs black. Patrick posted he changed plugs with no real improvement. But, hey... nothing to lose. More and more I'm suspecting the ignition switch. My car has gone through 4 of them. Engine starts up when cold and as the car warms up, I got from misfiring, to total ignition failure. Cheers Gary 79 MGB |
| gary hansen |
| With the engine running you should get the ignition warning light coming on if the ignition switch fails in all cases except North American 1977. On the others 12v output from the alternator goes through the warning light to the virtual earth through the coil and distributor. |
| paulh4 |
| Have some other errands today, but hope to try the +ve and -ve checks this afternoon (got the wires hooked up through the firewall and a voltmeter ready to check. Ignition light comes on when starting, and seems to stay on a little longer than before, but goes out once oil pressure goes up. Occasionally lights up when trying to stall in driveway after a short run. Anyway, hope to get at it again later today. |
| Patrick Callan |
| Paul, ready to try your test, but have a question. When individually testing the +ve and -ve voltages, are you connecting each side individually to a ground? If so, what numbers should I look for? I assume the +ve side should show somewhere in the 10-12 volt range, but am not familiar with numbers for the -ve side. Thanks for any additional info. |
| Patrick Callan |
| It's normal for the ignition warning light to come back on as you are approaching a stall, lower than 600rpm or so. The engine needs to be revved to typically 900rpm or so to get it to go off to start with, so not connected to oil pressure other than via engine revs.
Initially the voltages are taken with respect to earth. As a 73 and so unballasted ignition on the coil +ve you should see a steady 14v or so once the ignition warning light has gone out, dropping a volt or so as more and more electrical loads are turned on, but that is all. If the voltage is steady with the misfire then the supply side including the ignition switch is OK. But if it starts flicking down in time with any misfire it indicates there is a bad connection back through the white circuit. In which case move the wire to the white at the fusebox and try again. If it's not doing it now then the problem is between the fusebox and the coil, but that's obviously not very far. But if it's still flicking down then the next point would be the white at the ignition switch. Check all the connections here for security if you haven't already done so. Again if it stops doing it then the problem lies between the ignition switch and the fusebox, but if it's still doing it then connect your wire to the brown at the ignition switch. If the coil +ve shows a steady 14v with the misfire then move the wire to the coil -ve. The meter should now be acting as a dwell meter - switching between 14v when the points are open and 0v when they are closed. The steady voltage that would be displayed an an analogue meter, and some digitals, will depend on the points gap and will be nominally 9v on a 25D4 distributor or 8v on a 45D4. If you are using a digital and the reading is jumping all over the place then you will not be able to go any further. If you get a steady reading, and it changes when you get the misfire, then you can proceed. If the reading goes up with the misfire then that indicates that the circuit through the points is going open-circuit. But if the reading goes down then either the circuit through the coil is going open-circuit (unlikely given multiple coils) or the circuit through the points is going short-circuit. If the reading stays steady, then the problem is not the ignition LT, so I'd be looking at the HT and there are more tests that can be done there. You can tell which, by moving the earth connection of the meter to a 12v supply. If the reading now goes down with the misfire it is the coil going open-circuit. But if it goes up then it is the circuit through the points going short-circuit. In each case, as to why, will be the next thing to determine, but at least you will hopefully have narrowed it down. |
| paulh4 |
| Paul, thanks - that is a lot to absorb, but I hope to give it a try this AM. Will post how it goes. |
| Patrick Callan |
| Using a better voltmeter, the +ve reading is a steady 12 volts, regardless of rpm. The -ve reading is about 5 volts at idle, and goes up to about 9 volts when I increase rpm, but when I hold the rpm steady, the reading is steady. I did notice that when I hold the accelerator steady at about 2000rpm, the tach and audible rpm randomly spike upward, with no change in the coil voltages. Almost makes me wonder if the fuel pump is randomly failing to maintain a steady supply. |
| Patrick Callan |
| 12v is too low, if that's the voltage at the battery it isn't charging. If that's 14v then there are bd connections between the alternator and the coil.
Odd readings on the -ve, that's more like what you would get with a variable dwell electronic system. For points that indicates to me that there is a problem with them failing to keep up with the cam at higher revs. The increase in rpm when holding the throttle steady could be changes in timing, which could be caused by problems with the points or the vacuum advance mechanism. Clip on a timing light and see what that shows. Fuel pumps aren't required to provide a steady flow for carb systems, unlike for fuel injection systems. The pump just adds more to the float chambers as fuel is used. The level in the float chamber could drop quite a bit before you would notice it at the engine, and it would be a gradual change, not a sudden change at the tach that you have been describing. Did you do the delivery check? |
| paulh4 |
| These test are an excellent idea, particularly as they deal with the engine/car running in real life conditions of the road rather than static bench tests. But they do require the testing equipment to be reliable and reasonably accurate, the person using them have the knowledge and experience to connect the meter to the right connector locations and in the correct way. Photos and videos are better at illustrating how to do the test work and how it's proposed to be done or done. |
| Nigel Atkins |
| Re-cleaned the white and brown connections at the fuse box, and now the +ve side does read 14v. Also took a closer look at the meter, so my visual angle might have had an earlier impact, but it looks like 14 now. However, the -ve readings are the same as earlier. Idle seems pretty good - no tic's in the tach up or down. But at about 2000rpm the tach starts jittering again. |
| Patrick Callan |
| water in the floatbowls-? |
| William Revit |
| Use the dwell meter to see if that confirms the readings you are getting from the coil -ve i.e. different readings at different rpms.
Also do the timing light test when held at 2000 and the revs are jumping up. But really the coil +ve and -ve tests needs to be done while on the road to reproduce the sputtering under load you first mentioned. Also when you wrote "Occasionally lights up when trying to stall in driveway after a short run." did you mean you were deliberately trying to stall it on the clutch? Or it was trying to stall by itself? |
| paulh4 |
| Pat,
you're seeing the value in having all electrical connections clean secure and protected. Not associated here but this includes the sprung fuse holder connections inside the fusebox, both ends, and even the fuse both ends. Poor connections or wires, for whatever reason, can continue to work but restraint full and proper operation and become intermittent when combined with other issues. Having good clean, secure and protected connections and wires will help the full function of the important safety items like lights, wipers, blower, horns and with the much less important aspect of having the engine running and running well. |
| Nigel Atkins |
| Late to the party, but what did you mean by "the plugs are clean" ? Could it be that the mixture is running a little weak? |
| Chris at Octarine Services |
| Lot of suggestions to get to today.
Have not disassembled the carbs to check for water or float problems. Will check with dwell meter and timing light at various rpms. Difficult to check when driving - too erratic to get very far from the house, but will try again. Ignition light coming on when rpm drops below about 500 - will stall on its own unless I apply gas. Will resume contact cleaning. That appears to have made a little difference on +ve volts. When I mentioned clean plugs, I meant not fouled by carbon deposits. It was running so smooth before all this started, I don't know how mixture could have changed so rapidly on its own. Thanks to all for staying with me on this problem. |
| Patrick Callan |
| Patrick Easy little job for you MGBs have a drain plug on the bottom of the tank, easy to get at--leave the car sitting flat on the ground and reach in under there and drain half a litre or so and put it in a clear glass jar and check to see if it's milky or not, if it's ok you can tip it back in but at least you'll know if you've got a load of water or not-------- |
| William Revit |
| Ignition light comes on when revs drop below 500, it idles at 500 rpm, blimey. Does make me wonder how accurate or not your rev counter is, and now if it's original, what the number on it? Leads me on to how factory standard or not your car engine, fuelling and electrics generally are. |
| Nigel Atkins |
| This is getting more complicated with idle fluctuation as well as everything else. Tank drain plug - maybe, maybe not. Originally provided until 1974 according to Clausager, but the replacement tank for my 74 I had nearly 30 years ago did not come with one, and neither did the one I took off. The pickup draws fuel from almost the very bottom of the tank, so doing the delivery check mentioned earlier will also show you what it looks like, as well as checking for fuel starvation. |
| paulh4 |
| Sorry if I confused the idle and trying to stall info. The car has been idling pretty well in the driveway, but if I take it out, upon return (and warm), the rpms drop off way down, and it tries to stall. Erratic tach seems to be as rpms go up when applying gas. Will add another fuel check to my growing list. When starting, the ignition light goes out when rpms go above about 500. Sorry for confusion. Will try to be more accurate with my readings. Can I claim a "senior moment?" |
| Patrick Callan |
| That's the difference though the pickup is 'almost' on the bottom but the bung is on the bottom and if there's any water, that's where it'll be ,and Patrick's car is a 73 which is why it was suggested to check it at the tank and if it does have a fuel filter has that been checked, it's been mentioned by others on here but no reply on that while he's being led down this electrical trail
What I'd like to know is a more detailed description of spluttering on the road, when it happens can you drive through it with more throttle or does it get worse with more throttle Does it rev out or hit a wall on the road Will it rev out in neutral We have to remember this started after refueling so that would be the obvious place to start I know if I'd been driving along ok, stopped for fuel then it all went wrong I'd be looking at fuel first, eliminate a possible issue there first it's the most obvious cause------- |
| William Revit |
| Weather bad here right now, so can't open up the garage and move into the driveway to run and check dwell and timing.
No drain plug on the bottom of the tank, but I was able to re-check fuel at the carbs before rain started. Fuel flowing well into a container after the filter, and has no sign of dirt or water. Don't know why I didn't mention that earlier - having a lot of "senior moments" lately. The tach fluctuations are not present while at idle the last couple of times out. Maybe contact cleanup has impacted that. Fluctuation starts when I apply gas, with a loss of power if I am going up hill, requiring downshift. Back to testing tomorrow if the weather permits. |
| Patrick Callan |
| Whoops, I think you might be in trouble (not with me) :) "with a loss of power if I am going up hill, requiring downshift" Did you try pulling the choke out at this or spluttering? (but I'm probably pushing up the wrong hill - barking up the wrong tree). |
| Nigel Atkins |
| Try this: While in the driveway, have some one slowly bring the RPM's to the point of sputtering and hold it there. When it is sputtering, you armed with an insulated screwdriver, gently "jiggle" one wire at a time and see what happens. This is one the "10/10 fixes". 10 hours of diagnostics, and then 10 minutes to fix it. Cheers Gary 79 MGB |
| gary hansen |
| Ok so it's going uphill, splutters ,needs a downshift then what happens will it take the throttle in that lower gear and rev out or does it die off in that gear as well From a standing start on the flat does it die out in each gear at the same revs or is it only in top gear with the load on Should be a nice sunny day Sunday for a drive |
| William Revit |
| Starts misfiring when trying to accelerate. As long as I downshift, it doesn't stall, but trying to accelerate again and the misfires start again. Seems worse on a hill, but probably just more noticeable, because it misfires on flats as well during acceleration. Idling in the driveway does not seem to cause the misfire. I will try to validate (memory on symptoms starting to get foggy), but increasing rpm in the driveway does not seem to bring on the misfires. Hope to recheck dwell and timing today. |
| Patrick Callan |
| Patrick When you go for your roadtest- Just start off from a standing start and gas it, see if it missfires straight away under load at any rev or if it breaks down at the same rev exactly in each gear, just try and get a pattern of what it is actually doing, also try getting on the gass downhill as well and see if it breaks down then |
| William Revit |
| I must admit I had to look for it but I did put my usual (as I only know basic stuff) - that I'd do a service check, from tappets if not done recently, onwards as it follows a logical path to start checking and adjusting as required and go from there. Whilst doing this you can often spot issues, hopefully the one(s) causing the current problem. But Willy is now on a more direct path - however servicing if not done in a timely manner is always reintroducing on these cars. |
| Nigel Atkins |
| For me, you need to be keeping an eye on the voltmeter connected to the coil -ve when you can reproduce the problem on the road. Based on your most recent comments it could be fuel, HT or LT so we haven't got very far, but the tach jittering at the same time points (no pun intended) more to ignition. |
| paulh4 |
| Been thinking about this a bit Paul and I feel it's either going to be a condenser breaking down or dud fuel, the roadtest 'should' tell the story
If it's the condenser it's going to happen same revs any gear where the fuel will be more load dependant and he should be able to drive through it downhill- Your voltage test will of course pick up a faulty condenser-one of my v8s had a dud one once and it was just like a rev limiter at 3000 dead on in every gear, I thought it was the tacho causing it as it had a flutter at the same time but condenser it was I still feel it's fuel as he had just refilled but it may be a coincidence--we'll find out eventually |
| William Revit |
| The voltage test would reveal a shorting condenser but possibly not one failing open-circuit. I've never had one fail in 50 years, and only once fitted a new one years ago when I was 'treating' a distributor to new leads, rotor and points. Based on what others say about present quality I'd never do any of that again, and the majority of failures seem to be from internal connection failures i.e. going open-circuit, and once gone they stay gone. The only failure I've been involved with was one of those, and the car almost immediately became undriveable and had to be towed home.
Open-circuit it could well affect the tach, and others have said HT problems have caused that as well. Failure under load i.e. high demand CAN be caused by fuel starvation, but I don't see that affecting the tach, and we have to hope that Patrick has done a proper delivery check as mentioned a while ago. I can't see bad fuel causing problems under load when it doesn't at other times, nor affecting the tach. HT breakdown will cause problems under load, and could well affect the tach, but unless you can reproduce them with your head under the bonnet looking at timing light flashes, or HT testers on the leads, they are more difficult to isolate. |
| paulh4 |
| Paul I don't usually like advertising stuff on here but you being interested in this side of life might be interested in this link, easy to make up -- and the Zelscope download--fantastic for roadtesting (as a passenger) https://www.instructables.com/id/Use-Your-Laptop-as-Oscilloscope/ normal disclaimer-at your own risk |
| William Revit |
| A former neighbor had a Chrysler 225 "slant 6" idled fine. As the RPMs increased, the engine would backfire through the carburetor. Long story short, the secondary coil wire to the distributor was frayed internally. Replaced the wire, end of story. Next, 272 Ford V-8 ran great until engine got to operating temperature, then began to sputter and backfire. Replaced the new condenser with the old unit, problem solved. Cheers Gary 79 MGB |
| gary hansen |
| I have a lab oscilloscope and have done quite a few tests on ignition systems as well as other electrical circuits. Whilst I have a Win95 laptop (that I haven't used for years) I doubt anything produced recently would run on it. My desktop is XP, and having listened to hours of ranting from pals about how Microsoft updates have corrupted their Windows 10 machines I refuse to replace it! |
| paulh4 |
| Yeah I run a Bosch osciliscope in the workshop but having a mobile scope is handy for going up the road to monitor O2 sensors and the likes- interesting your comment on Win10, I've never had an issue with it at all |
| William Revit |
| I’ve had issues with MS updates slowing windows7 PC and laptop, but not windows 10 FWIW. |
| Dave O'Neill 2 |
| Hopefully some progress.
While examining and cleaning contacts, I decided to replace the line between the coil and the distributor. Also rechecked points gap. Engine fired up nicely and idled much smoother (although idle rpm was a little high). Went for a drive today and the power was back and running smooth. Thought I had the answer for a short run, but detected some slight "spits" once warmed up. However, there is no movement in the tach when I notice a spit. Back to the house, and idle was smooth - didn't try to stall. Put the dwell meter on to check idle rpm, and noticed that the dwell was reading low (below 50 deg). Tried to adjust the point gap, but can't seem to get the dwell above about 48deg. Difficult to line up the dizzy shaft. Might be my VERY old dwell meter, but the occasional spit/cough makes me think I still don't have the points gap set correctly. Anyway, running was a major improvement - hope I am at least on the right track. |
| Patrick Callan |
| OK..! This is good news. Next try your condenser. Adding to my previous post about condensers. 1966 Chevelle 194 c.i. 6, complete tune up plugs, points, rotor, condenser. Turn the key, engine cranks and cranks. replace condenser with old unit started right up. Cheers Gary 79 MGB |
| gary hansen |
| If you can get the gap down below 15 thou but your meter still shows less than 50 degrees then the meter is indeed faulty. Unless there is wobble in the shaft, which could result in all sorts of symptoms. |
| paulh4 |
| If the testing equipment is unreliable it's worse than not doing the test (as in the real world at the moment). I changed to a good quality fully electronic (bottom as well as top) dissy 11 years and tens of thousands of miles ago, fit and forget no farting about with it, better starting, idle and running throughout the rev range. Goes very well with a good coil (and plugs, and leads) Paul. :) |
| Nigel Atkins |
| Have a hard time believing that replacing the wire to the distributor and trying to adjust the points could have made that big a difference. The old dizzy wire had no breaks and resistance was fine - even if I wiggled it to check for internal breaks. I had measured the dwell before all this started, and it was rock steady at 60 deg. Not sure how it could have drifted off enough to cause such rough running. I guess it is possible that I have been chasing a bunch of smaller issues that added up to the problem, and that my dwell meter is getting flaky. I have heard that you can use a voltmeter to check dwell. That may be my next trial, and may even get to Paul's recommendation to look a -ve closer while driving.
I have another condenser that I can try, but I got all the dizzy "guts" from Jeff S, so they should be good. And I am a little nervous about trying too many smaller issues right now. If the condenser were gradually failing, wouldn't that be reflected in the tach? I keep repeating this, but thanks to all for keeping up with saga. Hopefully, I am close to the solution. |
| Patrick Callan |
| If you got the condenser from Jeff S then it 'should' be OK but if you swap it for another known good one no harm done (unless you disturb something whilst doing the swap).
You could contact Jeff S to confirm that when you got the stuff from him there wasn't a batch of any iffy parts, I've had this from a good supplier and they readily confirm this and help you out with a replacement - unlike Toss and others who'd sooner blame you the customer and of course "no one else has complained/ returned any". Replacing a wire, adjusting the points, bunch of small issues, all or any of these individually or in any combination can make a big difference. You're not sure about your testing equipment so previous confirmations with it mean very little. If you don't want to make too many changes at once then swap out items one at a time until the issue disappears. I can't remember have you swapped spark plugs (always a favourite with me) and HT leads - both regardless of how they look visually and show on test equipment. Easy and fast to swap these out one at a time it's the road testing after each that takes the time. Did you carry out Willy's tests and note results? |
| Nigel Atkins |
| Only if the condenser were going short-circuit would it be reflected in the tach, and the usual failure mode is open-circuit which results in a very weak spark and lots of arcing at the points. A second condenser temporarily connected between the coil -ve and earth - if that solved the problems - would indicate the condenser was indeed going open-circuit.
You should be able to use a voltmeter as a dwell meter - certainly an analogue type, digitals may vary. But I thought you had already done that and it showed a significant variation in voltage at different rpms when on the -ve, which I wouldn't have expected. I think I asked you to see if the same variation occurred with the dwell meter. I know that is suspect, but it would still be interesting to know if that gave a steady reading at different revs, or different readings as the voltmeter did. If the tach has stopped flicking then the voltage tests on the coil +ve and -ve are less relevant. |
| paulh4 |
| Patrick: These cars are 40+ years old. Wiring as well as other items deteriorated. Hopefully you're on the right path to a solution here.
Nigel: I also side with you on the electronic change over. After many "collapsed points episodes" I switched to a Luminition unit some 18 years ago without any problems at all. Faster starts, more power, and reliable. et al: Not to start a firestorm here, as far as condensers go, I don't know about the UK, but there have many "duff" units here in the states. Perhaps the UK has been fortunate enough to get better quality units than we have. Cheers, Gary 79 MGB |
| gary hansen |
| Absolutely not Gary, over here condensers and rotors have been so bad even the likes of Toss have been copying the ideas of the Distributor Doctor (our Jeff S) and selling better versions, whilst still selling the cheap crap versions the tight-fisted classic owners over here insist on.
I've also found poor quality Lucas green box dissy caps - I wouldn't know about points personally as I always remove them for at least a good quality igniter head, but now full electronic dissy, but I have seen many reports of crap CB points. Not those from 25+ years ago and I don't know about today but certainly in fairly recent years. http://www.distributordoctor.com/ Toss - condenser for the tight-fisted - https://www.moss-europe.co.uk/condenser-lead-gsc111.html?assoc=108958 Toss alternative condenser HQ!, and out of stock - https://www.moss-europe.co.uk/condenser-lead-25d-high-quality-gsc111hq.html?assoc=534797 Toss rotor - https://www.moss-europe.co.uk/rotor-arm-25d4-gra2101.html?assoc=108952 Toss copy rotor - https://www.moss-europe.co.uk/rotor-arm-25d4-high-quality-gra2101hq.html?assoc=108953 |
| Nigel Atkins |
| Ok, just got back from a MUCH better run. A couple of minor "coughs" but plenty of uphill power, and no movement of the tach on the coughs. Also re-ran my wire from the -ve side of coil to an analog voltmeter on the passenger seat. Tried to watch that as close as possible while driving, but the voltmeter seemed to be constant on the coughs as well. -ve reading looked like about 7.5v. I understand that should relate to dwell, but don't know what the formula should be. Connected the dwell meter when I got home - reading at 50 deg and steady at a range of rpms.
I did not try to readjust the points just yet. Going to research the -ve to dwell relationship to see if my dwell meter is reading properly. Warm idle seems to try and dip low a bit, but hitting the throttle quickly seems to bring it back to about 900 rpm. Thinking maybe I will put the newer plugs back on to try and get rid of the (infrequent) "coughs." Fuel getting lower, so I will also get a new fill up before long. |
| Patrick Callan |
| If your fuel is low why not try filling with fresh fuel and see if Willy was right all along.
You've found improvements so it seems that you had more than one issue or an accumulation causing an issue, especially if the tacho jitter has gone but a cough remains. A cough is different to spit to me and *could* be more fuel side BUT the general rule is most 'fuel' problems are actually electric side. When you stop this cough you'll have been tinkering quite a bit so I'd suggest you recheck and adjust if required the service chain, from (if required tappets), CB points, then plugs, then the timing, end with carb mixture and balance if required. Follow that order and if you have to adjust any item in that chain then you’ll also need to check, and adjust if required, all the items that follow it in the chain. |
| Nigel Atkins |
| Rubbish condensers in the UK as well, but people who have taken those apart say it's usually the wire losing contact with the foil i.e. open-circuit. With tach and voltmeter constant now including on coughs it's more likely to be HT or fuel. |
| paulh4 |
| Good drive this afternoon. Put a better set of spark plugs back in, and treated the car to a fill of high test gas.
Good power on hills, good idle speeds, tach nice and steady. Only one little cough when down shifting a a flat area of road due to a driver only going about 20 mph. Otherwise, no coughs/spits noticed. Still confused about a dwell angle of 50 deg, but that may be an old meter - maybe I have been adjusting with a bad meter for some time. Will update on any following changes. Thanks again to all! |
| Patrick Callan |
| Pat,
do you have fitted a clean or fresh fuel filter in engine bay, or an in-line or a filter in or at the fuel pump? If these spark plugs are only better then buy a new set of NGK and throw away the set that aren't better - are you saving struck matches in the box of unused matches, do you save blown fuses - I'd get your meters tested, and repaired if required and possible, or get good quality and reliable replacement(s) or you could, now and in the future, be chasing setting up ignition or faults in ever increasing circles, for evermore. |
| Nigel Atkins |
| Nigel,
I know - I hang on to everything. Fuel filter is good, and the fuel pump does have an in-line filter. Don't have new plugs or plug wires yet, but my son gets mad at me if I even go out for groceries these days, let alone a parts store. For now, I am happy with running well, but will update parts ASAP. Don't know if I can trust my dwell meter any more - may have to invest in a new one or borrow one from a neighbor to verify readings. Sometimes I already feel like your "evermore" warning. Talked to someone who recommended going to copper core plug wires, but they seem to come as a "kit" for one wire at a time - not what I had anticipated. |
| Patrick Callan |
| Pat,
have you checked both filters are clear and clean and not restricted in themselves or their fittings or installation. I don't think you should be buying new parts for the sake of it only replacing parts that need replacing (and disposing of previous dubious parts. I'm not a fan of buying items for delivery but it does ave its uses, especially now. Don't bother with copper wires as they could be restrictive to future improvements/changes and you'd need to 'suppress' them depending on your radio (and TV?). When you need to replace just get reasonable quality, usually they're not cheap but not expensive either. The problem with borrowing someone else's testing equipment is that often you don't know how accurate or reliable it is so perpetuating the 'evermore'. IF the 'cough' is very mild and very intermittent then try using more of the fresh petrol and the 'Italian tune-up' (after fully warming all of the car's systems each time). You've made improvements so things are going well - sorry about the purchase of the coil, keep it and the previous one but get rid of the coil before that. :) |
| Nigel Atkins |
| Seconded on not using copper-cored HT leads.
Get basic silicone-cored for under £20 or equivalent, the ones on my V8 have done 25 years and 120k and still have consistent resistance readings. There are rip-offs out there promising the earth, massively thick with fancy innards, for prices up to £100 or more, such as "creating sparks that are 300 times more powerful, reaching temperatures of 100,000 to 150,000 degrees F, spark durations of 4 billionths of a second and currents of 1,000 amperes magically developing from built-in capacitors". Check them before fitting as manufacturing faults can affect anything these days, should be about 6 to 8k ohms per foot (depending on the trustability of your meter ...). On a pal's TR the silicone core was hanging free of the metal connector meaning the spark needed to jump a much bigger gap that in should, and tested open-circuit. |
| paulh4 |
| You all convinced me to stay away from the copper core plug wires. Great drive today - no coughs/spits/misfires, even on hills. I am afraid to touch anything more right now. |
| Patrick Callan |
| Seems you got it !! These cars need to be driven. The more they linger, the more problems find their way into your car. Cheers Gary 79 MGB |
| gary hansen |
| Agree, enjoy driving it for a good while, being static isn't good for the overall running of the whole car. If it's running very well in all conditions then wait until your next service before touching the engine, ignition and carbs again. Apologies to Allen as he first mentioned bad fuel, but so did Willy - both wrong of course as driving the car sorted it! I'm joking. :) Just enjoy driving it. |
| Nigel Atkins |
| Several days of nice drives. Hope that is a good sign. If there is a draw-back so far, it is a kind of rough starting. Almost like it doesn't want to be choked. As soon as the pressure goes up and the ignition light goes out, it smooths out, but while the ignition light is on, it is rough (only about 10-20 seconds).
RPMs still drop when I get back home, and coast (or drift in first gear) into the driveway. Up to that point, idling at stops on the road seem to be fine. Maybe it just doesn't want to get back into the garage. |
| Patrick Callan |
| My bad - rough starting more like 5-10 seconds while ignition light is on. |
| Patrick Callan |
| If it's definitely associated with the ignition warning light the implication could be that not enough power is reaching the coil until the alternator starts charging, but ordinarily I'd expect that problem to affect cranking as well. Try dragging the idle down by trying to stall it in gear until the warning light comes back on again and see what that does. It could also be associated with whatever you are doing with the choke when cold starting. |
| paulh4 |
| Cranking does not appear to be a problem. Drifting a very short distance down hill into the driveway while in first gear does drag it down, light comes on, and it will stall unless I give it gas. That has been occurring for quite a while before other issues in this thread started. Drifting to stop at a stop sign/signal in gear while out for a drive does not drag rpm down. Will try varying how choke is applied. |
| Patrick Callan |
| Holding the clutch pedal down will tend to reduce idle speed if you have a graphite clutch release bearing, some cars seem to do this to quite a marked degree and others virtually not at all.
But if both situations regularly generate the same effect, when you are rolling in gear with the clutch pedal down, and the car fully warmed up in both cases, then something else is afoot. This reminds me of the car that wouldn't hot start when the owner bought vanilla ice-cream, but did when he bought chocolate chip! And there was a reason for that. |
| paulh4 |
| Tried starting without choke. Same rough start until the ignition light went out. Then idled a little low. Engaging the choke slightly brought rpm back up and smooth. Did not have to leave the choke engaged very long.
Smooth idling throughout a country drive - at stops and lights. Excellent drive. Back home and drifting into the driveway in first gear - rpm did not drop as far as previously, but did drop. Both stepping on gas or using a little choke increased rpm. Releasing gas or disengaging choke returned to a good idle. Since this does not seem to happen while out driving, I'm thinking to switching to vanilla ice cream! The car obviously does not want to go back into the garage. |
| Patrick Callan |
| Patrick: One thing to check. There are six 1/2" stud nuts which hold the manifolds to the cylinder head. Check the tightness of those nuts. You may have a vacuum leak. BTDT. Paul: The story I got from a GM Service Rep about the vanilla/chocolate ice cream was a 1966 Pontiac Catalina 389 V-8 2bbl carb. In the end it had to do vapor lock. Cheers Gary 79 MGB |
| gary hansen |
| Gary, Stud nuts all tight. Haven't given up looking for vacuum leak but so far have not found one. |
| Patrick Callan |
| Patrick: My MGB gets a bit "fussy" at a warmed up idle at times. I just attribute it lack of "exercise". On balance, the car runs very well and just live with its eccentricities. The more I drive it, the better it runs. Cold starts go off in a snap. Pump the gas twice after the fuel pump has finished its tic-tic-tic, and tap the starter and we're ready to go. Hot start may take a bit more "starter grind" but it does start. Just drive it. Cheers Gary 79 MGB |
| gary hansen |
| Gary, what do think pumping the accelerator pedal twice before you tap the starter achieves? Mike |
| Mike Ellsmore |
| Probably pulls the sticky throttle shafts/levers up to the opening needed for a start - would be better to free off the controls so that the throttles closed fully all the time and then adjust the idle. I see this a lot - also indicated by a high idle when hot which is returned to normal with a quick blip of the pedal. |
| Chris at Octarine Services |
| It's a hangover from fixed jet carbs with an accelerator pump. I have to say that I can't see SU carbs failing to open a sticky butterfly if you can pull the choke or push the throttle pedal. Sticking open when releasing them yes, and pushing the cams back down onto the idle screw stop when there is a high idle to check for that was one of the first things suggested waaaaay back. |
| paulh4 |
| Sounds like your idle mixture is too rich First sign is that it starts cold and idles (although rough) without using the choke and second sign is the idle deteriorates after a run hot If the car wasn't right up to temp properly when you adjusted your mixtures it will undoubtedly be too rich when it does get there -unless you were using a co or a/f meter to set it--------- Like a lot of US cars Gary's car 'may' have had a little d/d Weber fitted-? --------------or not |
| William Revit |
| Yes, my car has a d/d weber. Cheers Gary 79 MGB |
| gary hansen |
| William, When the rpm starts to drop (usually in my driveway), I can bring it back up with the choke. That seems like it is not due to over-rich setup. I did notice that the rpm with the choke at the fast idle position goes to about 1100-1200 rpm. Idle during my drives is smooth at about 800 rpm, which seems good. |
| Patrick Callan |
| Patrick
Pulling the choke a bit to make it idle does nothing to prove mixture All you're doing by pulling the choke a bit is pulling the choke idle speed ramps around and lifting the idle speed, it isn't till you pull the choke further out that there is any significant enrichment Normally it is very hard to get a properly set up HIF equipped car to start cold without using the choke---If yours starts and idles ,although rough , cold without the choke, then your idle mixture is in my opinion too rich If you go to adjust the mixtures , be aware, they adjust back to front to most carbs, turning the screws clockwise richens , anti clock leans willy |
| William Revit |
| How have you got the fast idle set?
HIFs have an engraved line on the cam, and when that is under the fast idle screw that is the start of enrichment. Normally that would equate to the control being pulled about 1/2". The fingers that fit in the small hole in the cam are clamped to the interconnection shaft, and they need to be adjusted independently to position the engraved line the same on both carbs. Then the cable needs to be adjusted to get the correct movement of the control knob. The same principle applies to the throttle. Cold starting without choke, but runs rough unless the choke is pulled a bit, says to me that one of the carbs is too rich which enables it to start, but the other is weaker causing the rough running unless both are enriched with the choke. I.e. the carbs are unbalanced, and should be set up from scratch. |
| paulh4 |
| Bringing the choke to the lineup Paul describes increases the rpm (when warm) to about 1200rpm and smooth.
That position is lined up on both carbs and the linkage reacts the same on both. The carbs are nicely balanced (unisyn sp?) at both idle and fast idle. I used to adjust mixture with a Colortune, but gas with ethanol does not seem to work well with that unit. Will have to apply another method. I hate to get too deep into mixture changes because the car is running so much better. Next starting, I will apply full choke and see what that does. Will also recheck plugs and see if I can identify an over-rich carb. |
| Patrick Callan |
| Pat, I think you're right to first try gradually applying choke (rather than fast idle) to see what happens before going further. I also agree with the Colourtune not seeming best way to sort things - not that I know much about this, just never got the Colourtune. Paul has a good point about linkages but cable pull length at knob is probably best at what you're used to provided it's all operating properly. |
| Nigel Atkins |
| Best to remove the dashpots and set both jet tubes exactly the same depth from the bridge and check that the needles are fitted to the pistons correctly for a good starting point And in case you're not aware HIF carbs have their idle mixture screws attached to a temperature sensitive bimetal strip making it super important to make sure the whole engine is right up to running temp before attempting to adjust the idle mixture, If you don't, when it gets hot the mixture will change |
| William Revit |
| As I understand it the temperature control is there to maintain the mixture as the fuel viscosity reduces with heat. When running the carbs will be pretty cool, heating up after switch-off, which is probably means the engine should have been running a bit to stabilise after a hot restart as well as more obviously a cold start. All carb types need the engine to be at normal running temperature before you attempt setting-up. |
| paulh4 |
| Ok, easiest check first (especially on a rainy day). Removed each plug. They are carbon blackened - cleanable and dry, but definitely running a little rich. I guess the good news is that all four plugs were identical. Hope that means my balancing efforts have been correct. May try leaning one flat on each carb before my next run. Will see if that makes a difference on startup as well. |
| Patrick Callan |
| Not sure a "flat" is not the correct for the mixture adjustment screws. Maybe 1/4 turn? |
| Patrick Callan |
| Yep-anti clockwise =lean
It would be better if you took the dashpots off and equalised the heights to start with , but I guess if all your plugs are the same colour they are probably fairly close Once you get a decent colour on the plugs you will be able to fine tune one carb or the other to equalise the colour if there's a mismatch And don't forget- plug colours will darken up with short running or after using the choke, so a good blast out the road ,pull the plugs on the side of the road and have a look then as well With the colourtune- did you have it blue or flicking between blue/yellow---A friend set his E type up by their specs ,blue, and it was stinky, I poked my co meter up it and it went 8% which is way too rich, we wound it back to just 4% and it cleaned it up and just out of interest put the gunson c/t back on and it was right on the changeover between blue/yellow |
| William Revit |
| Or even 1/8 turn when using the lifting pins, even 1/4 turn is pretty coarse in practice. |
| paulh4 |
| Back before the onslaught of ethanol, I could use the Colortune, and tried to set it just at the blue/yellow change, but with ethanol in the fuel, it became difficult to watch for color. Not sure I can easily move the screws 1/8 turn, but will give it a try. I was actually pleased with how equal all the plugs looked. Hopefully that means balance settings are close. |
| Patrick Callan |
| Pat,
have look through all your suitable sized screwdrivers and find one where you can clearly mark out on the handle at least quarters (90 degree) that way halfway between the marks will be the 1/8 and have a defined start mark on one of the quarters so you can count from starting position. Also have pencil and paper to record what you do each time to each carb as jumping from one to the other you can forget and it means you can return to a base level, or where you were before you started if all goes wrong, if required. Personally I'd also have in big letters at the top of the paper, or a diagram, anti-clockwise = lean, or whatever words or expressions you usually use. I was helping, well actually watching, a nieghbour with his HIF twins when he looked up and asked what he'd done just altered the other carb to and neither of use could remember so both carbs had to be set back to a base line and start again. |
| Nigel Atkins |
| I use a flat-blade screwdriver and it is easy to get it near mid-way between vertical and horizontal and vice-versa. A bit less so perhaps if it is not starting from one of those three positions, but then it's not paramount to end up at an exact multiple of 1/8ths from the starting position. |
| paulh4 |
| What!! I think we've had enough of uncalibrated instruments! You could be 180 degree out at the very start with an unmarked flatblade! |
| Nigel Atkins |
| Ok, 1/8 turn lean on each carb over the weekend. Like the idea of recording each step - helps my senior memory. First drive today. Full choke to start - no roughness. Smooth transition to fast idle, then choke off. Nice drive - good power on hills remains. Idle speed at stops excellent and smooth. Then the drift into the driveway - yikes, a smooth idle with no attempt to stall. Will check the plugs once they cool down. |
| Patrick Callan |
| Plug check this AM. All four plugs look identical - no carbon buildup, light tan color. Look like lean burning. Guess it might be time to stop fiddling and back to driving! Thanks yet again for all the good info and recommendations. |
| Patrick Callan |
| Well done.
Yes stop fiddling, more driving and the whole car can get better - soon be good enough you enjoy the drive and stop looking out for if things are going well. Don't be afraid to come back here with other problems (or, hush my mouth, if misfire comes back). Cigar to Willy. BTW - the recording is a good idea but you do have to remember to do it, and have pencil and paper handy (and calibrated tools) and then remember where you put them all down, and go back to the same place you've just looked to find they're still not there. By coincidence, I was seeing if I could get a test on some HT leads I have and the cheap digital meter showed silly figures on Homers but had figures come up on the continuity setting so I recorded those and then tried to repeat the test with me and the leads more relaxed and the meter went intermittent. So I done what I should a long time back and go out the electronic mobile device repair kit, 2lb lump hammer, that resolved the problem. I thought about taking a photo for Paul but couldn't be bothered wrestling with my old digital camera. |
| Nigel Atkins |
| Thanks Nigel. I have to correct my last post - should say "looks like clean burning" as opposed to "lean". Hate those auto correction things. And I was very pleased that all four plugs looked the same. And I sympathize with the notes to "seniors" and memory. |
| Patrick Callan |
| I did wonder about the "lean", but as I'm king of typos I allow a bit of latitude. My problem Pat is that I'm old but not that old, my mind and body seem to be well advanced of me chronologically - perhaps it just means I'll be more used to it when the calendar catches up. :) I hope Paul realised my comments about an uncalibrated flatblade were jokes - I didn't put smilies again. :) |
| Nigel Atkins |
| Another great drive yesterday afternoon. I really appreciate all the great advice and recommendations from members of this forum.
Step by step addressing of things from jittery tach during sputtering, to cleanup of contacts, to plug checks, to mixture settings. Each one lead to what I hope is a fix. Not sure if any one issue was the original culprit, but they sure totaled up to a running problem. Much smoother right now. I even think is sounds better, and definitely idles better and accelerates better. Thanks again for everyone who stuck with me through this issue. |
| Patrick Callan |
| Well done.
I often think there can be a combination of small issues that on there own wouldn't perhaps be that noticeable but combined cause upset to each other and overall. Some people like to laser in on the one thing that is causing the problem and not attend to other related items at the same time. Like checking all the electrical connections rather than those immediately to the area of suspicion. For engine running that's why I like the idea of at least checking the simple service set up chain of tappets, points, plugs, timing and mixture in that order as you can often find the issue or other issues. It's easy to forget what it sounds like for the engine to be running well but when you get it back you know it's been missing. Best you do a few more runs to get the sound fully locked into your memory. :) |
| Nigel Atkins |
This thread was discussed between 17/04/2020 and 31/05/2020
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