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MG MGB Technical Back to basics: What causes a miss. BBS discussion at MG-Cars.net
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MG MGB Technical - Back to basics: What causes a miss.
| I need input before I go nuts. As I have posted previously, I am getting a 79 spitfire back on the road. Car has 55,000 original miles and sat in a garage for 10 years due to a hole in the radiator. Compression is between 130/134 in each cylinder. Allison electronic ignition was replaced with a 25D distributor. (miss was present with the Allison also). ZS carb replaced with a single HIF 4 SU (ZS was running rich and after two rebuilds, one by a british car shop, it was still running rich.) Valve train appears correct and valves are set to 0.10 per factory specifications (I have not pulled the rods but do not see any that look bent) All original wiring. Only wires not connected are the electronic ignition wires that went to the distributor. New coil, new cap, plugs, rotor and wires. The exhaust and intake manifold were checked for cracks/leaks by filling each with water and let them set and did not find any leaks. Car has all smog equipment and all parts appear to be working. Air pump is pumping, valve in the pump line is sealing correctly. EGR is functioning. All canister lines are correct and the canisters were refreshed with new charcoal. Fuel return system is open and working (no pressure when I open the gas cap.. Catalytic converter insides look good. No breaks in the honeycomb. Have sprayed starting fluid on every inch of the vacuum lines, manifold, hoses,and connectors. Sprayed around the carb and throttle and choke shafts, and cannot find any vacuum leak. Timing is spot on 10 degrees BTDC. I have adjusted the HIF per instructions multiple times. Float is set perfectly to factory specifications. Plugs show a light tan color. I have put a spark tester between the plugs and the wire and cannot see any miss in the spark (miss is very irregular). Have replaced each spark plug wire one at a time. No matter what we do, the car still has a miss. This is visible on a secondary tach meter and also audible in the exhaust. Miss is not rhythmic and runs throughout acceleration. So help me out here. What am I missing. What causes a simple motor like this to miss? I will take any thoughts at this point. |
| Bruce Cunha |
| Is the head warped at all? Hole in rad may have caused serious overheating back then. |
| S Cole |
| Bruce, Looks like you've covered all the bases, and it might be time to use a vacuum gauge to do a little troubleshooting. This may provide a few clues as to what may be happening inside the engine. http://www.gregsengine.com/using-a-vacuum-gauge.html Regards, Larry C. |
| Larry C '74 B/GT |
| Thanks Larry. Only thing I see as an issue is the the 79 Triumph does not have a manifold vacuum port. It takes its vacuum off the carb forward of the throttle plate. I will look it over to see if there is a port on the manifold I can use. As for the head. Owner said he picked up a rock but the leak was minimal and he only found it was leaking when he noted there was water on the floor the next day. So it did not sound like it got hot. The motor fires up quickly once warm and has good power/acceleration. No water in the oil, and compression is very consistent in each cylinder. If a warped head is a potential for causing a irregular miss, It is not a hard head to pull. |
| Bruce Cunha |
| Bruce, A vacuum gauge should help at least determine if it's a head gasket, or another problem. Are their blanks in the intake manifold that could be tapped for fitting (later to be capped)? Good luck mate, you have a good one there. Larry C. |
| Larry C '74 B/GT |
| Bruce Want to help you here but a bit confused You mentioned "No matter what we do, the car still has a miss. This is visible on a secondary tach meter and also audible in the exhaust" then "The motor fires up quickly once warm and has good power/acceleration." When does it actually miss- When you say secondry tach meter-do you mean a scope If it is a scope is the missing cylinder the same one all the time--is the spark line shorter or longer than the others when the missfire is doing it's thing willy |
| William Revit |
| Bruce, Here are a few more thoughts from the MGA Guru that may help. You mention an SU HIF-4 replacement. Was this a recent re-build, or new? Could the needle and jet be causing a lean mixture for this engine under load? http://mgaguru.com/mgtech/care/cf106.htm Larry C. |
| Larry C '74 B/GT |
| Bruce, Kind of a long shot, but something else to do would be to run a leak down test on it. I can't explain why, but once I was working on a Porche that did well with a compression test but seriously failed a leak down test. If anyone knows how this is possible, I would still like to know. It was actually running on 3 cylinders, so it was worse than your symptoms. Charley |
| C R Huff |
| My money is on the low tension side of the ignition system. Since the miss registers on the tach, this would be where I would concentrate my efforts. RAY |
| rjm RAY |
| I'm still interested to know what is meant by a "secondry tach" and does it show on the tacho in the car willy |
| William Revit |
| Willy, I believe Bruce means something like a hand held tach connected under the hood, which is used for tuning purposes. I also think Ray is likely onto it with the low tension & tach stumble relationship. Charley |
| C R Huff |
| I was hoping the fact the tach/dwell meter, which is hooked to the distributor side of the coil was an indication that the points were bad. Replaced the points with a new set from advance distributors and also changed out the rotor and the condenser with advance distributors parts. Fired up a bit easier, but still has the pop in the exhaust Here is a recording of what the exhaust sounds like. Can I measure the lift on the cam by setting up my magnetic dial indicator gauge over each valve and turning the motor over? I don't think it is a valve issue, but it is worth a shot. As for low tension leads. All under the distributor are in good shape. The points have a plastic bold on so I am not grounding out the condenser or low tension lead. Lead from coil to distributor is a new wire with soldered terminals. https://www.dropbox.com/s/hluop6tdytcat8v/spitfire%204.mp3?dl=0 |
| Bruce Cunha |
| Here is a video of the motor running at 900 rpm. As you can see. It runs smooth. The valves in this video are not tight. We were getting it ready to smog and having the valves loose reduces the hydrocarbons. It sounds the same with the valves loose or tight. https://photos.google.com/photo/AF1QipMXSTWgTf4a1eNHsBox1Wo3WF4zHDGtfozjRimQ The recording also sounds louder than the motor is. |
| Bruce Cunha |
| So, a vacuum leak is still a potential even though I have gone over every place where there is a potential for vacuum and have not found anything. I will be doing the leakdown test tomorrow and also check the lobes of the cam. The fact that the tach/dwell meter is hooked to the coil on the distributor side and shows slight deflection when the car misses gives me thought that this is electrical but as we have new points, rotor, condenser, plug wires, plugs and a new coil, I have no clue what else to check. I have even jumped from the hot side of the battery directly to the coil, hoping the issue may be in the ignition circuit wires. It did not change the miss.' |
| Bruce Cunha |
| Bruce, Have you watched it run in the dark to see if you can see any spark escaping? Charley |
| C R Huff |
| Bruce, Have you watched it run in the dark to see if you can see any spark escaping? Charley X2 Herb |
| H J Adler |
| Bit hard to tell but it sounds more like a spit out the exhaust to me from what I can hear I'd be having a real good look at the cam followers while you have them out If one has worn out of true it can hold the valve open occasionally as it spins around and creates a tight spot / no tappett clearance When it's idling do the rockers make different sounds as it misses---usually if it's a follower problem it will go quiet and miss then run ok/rattle in cycles willy |
| William Revit |
| Bruce, you may be experiencing a sticking valve. The fact that the car has sat for 10 years makes this a more likely problem. One of the valves may be occasionally sticking in its guide. This condition is often found in an engine that has been idle for a length of time. Rust or carbon can build up on the valve stem and hold up the valve so that it doesn't seat. A loss of compression follows. It will make the miss very difficult to track down. RAY |
| rjm RAY |
| A valve issue is a potential. Other than taking the head off, any cure for a sticking valve? When I had the valves set perfectly, I did not notice any noises from the valve train, but as you can hear in the recording, the pop is very irregular so a slight stick may not be noticed. Would a sticking valve come across in the electrical system? I can clearly see a deflection on the tack/dwell meter each time it misses. Not a hard job, but I was hoping I might not have to take the head off. If I can't find another reason for the miss, that may be what I need to do. I am going to check the cam height on each lifter today. Oh, and yes, ran it in the dark and cannot see any issues with spark. |
| Bruce Cunha |
| Bruce, you mentioned the ZS carburetor was running rich after 2 rebuilds. A bit of a long shot, but check the new plugs and see if the rich ZS possibly fouled a spark plug. Cheers Gary 79 MGB |
| gary hansen |
| Bruce The missfire, if it's mechanical, should not effect dwell but naturally you should see a drop in revs on the tacho as it misfires but there are different types of tacho readings If it's mechanical it will simply drop a bit while missing but If it's electrical it will depend on if the miss is caused by primary or secondary electrics and also if your tacho pickup is reading the primary or secondary electrics If your timing light is of the type that clips onto a plug lead you could try it on each of the leads in turn and see if you can pick up if the light misses when the engine misses on one of them to find which cylinder is giving you grief-------if it's electrical willy |
| William Revit |
| " This is visible on a secondary tach meter " You would have to have a very accurate tach to see a drop in engine speed from a misfire, and I can't see any 'fixed' defect causing an irregular and occasional misfire like this. It's almost certainly an ignition problem, and whilst you would definitely see a missed LT pulse on the tach, I believe you will also see a momentary short-circuit i.e. HT breakdown to earth on the tach as well, as that changes the HT characteristics which reflects back into the LT. If it is ignition, then you should see a missed flash on a timing light especially at low revs and definitely at idle, in which case you should be able to determine whether it is all plugs and hence rotor or earlier, or just one and hence cap and later. The only other cause of a flick in the tach but no missed spark is if occasionally a spark is occurring sooner or later than it should. A timing light pointing at the crank pulley would hopefully show that. Another thing is to earth each plug lead in turn, and leave it idling, to see if it stops. I've used an oscilloscope on the ignition in the past - purely out of interest, and very interesting it was. The WSM has traces from a Crypton (or similar tester), and if you can find an old-school place with one of those it should show missing and extra sparks as well as low and high voltage, and even how the HT varies with combustion chamber pressure i.e. blipping the throttle. |
| paulh4 |
| Paul, when I worked at a service center, many, many moons ago, we had access to two high quality oscilloscopes that showed everything that was going on in the ignition system. I was able to troubleshoot a lot of difficult to diagnose problems with these units. Unfortunately, today these units are considered relics and are hard to find still in service. After all is said and done, I still think that the problem lies in the primary ignition system. RAY |
| rjm RAY |
| I still have my Bosch scope---use it all the time You can't do a proper tune without one That's the difference between doing it at home or going to a pro. One minuite on the scope will tell you exactly where your missfire is living But I also agree with the personal value of doing it yourself if that's what lights your bulbs willy |
| William Revit |
| Gary. I changed the ZS over for an SU HIF 4 after the second rebuild at the recommendation of the local British car shop that did the second rebuild on the ZS. I have a spark tester that goes in between each plug an lead wire that visualizes the spark. I do not see any fluctuation in the spark, but again, the miss is so infrequent and short that I don't know if you would see it. I can try the timing light and look at it a bit closer. I agree, I need an oscilloscope. I will have to check around to see if any shops have one in the area. The primary item that I don't know about is the smog system, Air pump pushes air into the exhaust manifold, I assume to assist the catalytic converter. EGR opens just briefly when the engine starts to accelerate and allows exhaust gas to be re-burned in the engine. Cant see how this would cause a miss, but again, I don't know these systems. As the sound recording shows, there are periods where the car runs correctly interspersed with an irregular miss. Back to checking wires and grounds I guess. |
| Bruce Cunha |
| Bruce, reading your last post you mentioned EGR valve. I had a 1976 Pontiac equipped with an EGR valve that would cause a stumble/surging. Try disconnecting the EGR and other smog equipment. Then run the car. If it still misses, then you just at least eliminated another suspect. Some of this smog stuff can be problematic. Cheers Gary 79 MGB |
| gary hansen |
| Bruce, I don't recall you mentioning anything about the high tension leads. Have they been replaced or checked for resistance. Also, do I remember correctly that combining resistor wires with resistor plugs can cause a problem? I realize that the tach would indicate a low tension problem, but a lot of that has been checked already. Charley |
| C R Huff |
| Thought What plug gap have you got and also are all the plugs exactly the same colour------- |
| William Revit |
| Again I can't see a problem with air pump, egr valve etc. that causes a single miss being visible on a tach. See this from NGK regarding resistor plugs in series with resistor leads: "As well as reducing electrical noise for radio, television and mobile telephones etc, many modern ignition systems require resistor plugs to stop electrical noise from interfering with the vehicle's on-board electronic control units (ECUs). If non-resistor plugs are used in place of resistor ones, the result can be malfunction and in some cases immobilisation of the vehicle. Resistor spark plugs should always be fitted, therefore, where specified. NGK resistor spark plugs contain a single ceramic monolithic resistor of approximately 5000 ohms. Because of the type and construction of the resistor (i.e. no springs), the problems of vibration and sudden changes in temperature that can occur with some other brands do not apply. The function of the resistor is to reduce electrical noise generated by the ignition system. The most effective place to situate a resistor in the high tension circuit is as close to the spark plug as possible. This makes the spark plug an ideal place to house the resistor. Because the resistance value is only approximately 5000 ohms, there is no detrimental effect on engine performance, power output, vehicle emissions etc. It is also a fact that many motor sport world champions only use NGK resistor spark plugs. In nearly all cases - apart from some very old low output ignition systems - resistor spark plugs can be used in place of the non resistor versions." I.e. not needed in an MGB, but shouldn't cause problems. |
| paulh4 |
| Put the car on a diagnostic meter today (a Pensky that I won at GOF central and forgot I had). It diagnosed a high point resistance. In checking, one of the connections for the low tension wire from the coil to the dist. was loose and not soldered well. I replaced this with a better wire and connectors, and installed a new plastic input lead on the distributor (another advance distributors part). Unfortunately this did not change the pop/miss. The better diagnostic meter shows that the pop is not associated with a change in tach. While the rpm does slightly change, I can't correlate this to the pop in the exhaust. Plugs are all a light tan color. gap is 025. High Tension wires are new. I am starting to think this could very well be a sticking valve. Perhaps some rust has built up that periodically keeps a valve from seating. The pop being the full pressure from the cylinder being pushed out the exhaust. My plan is to disconnect one spark plug lead at a time and see if the pop stops or changes. While the engine will not run well, it should change the pop when I find the bad cylinder. I am also going to put a camera into the cylinder to see if I can get a view of the valves. If I find something with this test, it is not all that hard to remove the head in a spitfire. One of the nice things of a tilt up hood is there is lots of room to work on the motor. |
| Bruce Cunha |
| You may be able to spot a sticking valve with an adjustable timing light. By connecting it to a suitable plug lead, pointing it at each valve in turn, and adjusting the dial appropriately, you should be able to 'freeze' the valve anywhere between fully up and fully down, then watch foe a departure from the norm when the pop/miss occurs. A noise in the exhaust from a missed combustion i.e. ignition should be different to one from a valve sticking open i.e. getting some of the combustion in the exhaust. Rather than disconnect plug leads you should earth them, or perhaps better still connect the lead to a spare plug laying on the block. A disconnected lead will result in a very high HT pulse which could damage coil, rotor, cap etc. Noting carefully how the pop/miss changes will be crucial. But it is getting harder and harder for those not able to hear it to diagnose further, as we are dependant on your descriptions of a noise. |
| paulh4 |
| Not all that uncommon for any engine, but that one will start valves bending when run with no coolant, or even tweak a guide. Your pal may not have been watching the temp gauge when he last parked the car and then found a little coolant on the ground to discover the hole in rad. Or maybe the temp sensor is located such that coolant low enough will give a false reading and he thought all was normal at shutdown. Or maybe the kid trashed it and played dumb about the hole in the rad? You have checked everything else. Those are fun cars, so worth some effort. Too bad is needs to be smogged in CA. What year is exempt, 1975? |
| S Cole |
| At this stage I would try another set of sparkplugs OR- just out of interest try it with the plugs closed up to something like .015" and again at .035" and see if there is a different result Although your plug leeds are new it doesn't necessarily mean they are good, varying the load on them by varying the plug gaps for a try MIGHT show something up Are they wire leeds or carbon string type With a multi meter you could measure their resistances from the posts inside the cap to the plug end fitting What sort of fitting is it where the leed fits into the cap ,push in or screw in willy |
| William Revit |
| Bruce, Just for curiosity, could you post a few detailed photo's of the engine bay itself for us? Larry C. |
| Larry C '74 B/GT |
| Thanks all. Put new plugs in this week. My diagnostic meter does do resistance for plug wires. I will check this also. I will get some additional photos of the engine in the morning. Paul. That is brilliant. Never thought of using the strobe to freeze the valve train. I do use an adjustable timing light so this will be an interesting test. Thanks for the point on not running with a lead off. I can easily put a plug on the lead. What about sound? I have an automotive stethoscope. If I listen above each spark plug, I would think I would hear a different sound in the cylinder when the pop occurs. If I do find a sticking valve, what are the thoughts about pressurizing the cylinder, removing the valve spring and then spinning the valve with a drill to seat it. Any dangers in doing this? |
| Bruce Cunha |
| "Or maybe the temp sensor is located such that coolant low enough will give a false reading " In my experience with a couple of coolant leaks the temp gauge will give no change in indication for coolant loss. I had a bottom hose pin-hole on the V8 on a motorway and the only symptom was a very slight misfire when accelerating. That was enough to make me pull in to the next services, which was a few miles, and by that time most of it had boiled out but the gauge was still in the normal range. When I had another problem that slowly pushed coolant out of the expansion tank overflow I fitted a level sensor, and even though that fault was fixed years ago I've never been able to bring myself to remove the sensor. William's tests with different plug gaps is a good one - that should show up a marginal HT break-down problem. I wouldn't rely on air pressure to hold a valve up if you are going to spin it. Depending on how patient you are you could wind a piston down and feed string/cord through the plug hole, then gently wind the piston up to press it against the valves. |
| paulh4 |
| Mate Be carefull with the stethescope Some or them have reinforced hoses and conduct electricity quite well Ask me how I know--- I was checking for an exhaust manifold leak on a F series Ford ambulance and brushed past the end of a sparkplug and man was that a big wack in the ear Took ages before the hearing came back properly Not nice willy |
| William Revit |
| William - OUCH. Point to remember. Ok so for today's diagnostic work. Pulled each plug wire (grounded the wire) and listened to the exhaust. I could not detect any pops interspersed with the rhythmic thump of the non-firing cylinder. Listened using a automotive stethoscope at the base of each spark plug, on each cylinder exhaust manifold port and each intake manifold port. No unusual noises or pop's were heard. (I had a person at the exhaust telling me when they heard a pop in the exhaust) Measured the height of each valve with the lifter at the open position. 5 valves measured 1" 15/32. 2 valves measured 1" 14.5/32. and valve 8 measured 1' 14/32. Is a 1/32 lower valve significant? Tried the timing light on the valve. Could not get it to freeze the valve. So, given I cannot hear any pop in the cylinder, could this be ignition of un-burnt fuel in the exhaust pipe from the catalytic converter? Is that even possible? Last, I ran the engine at 2800 rpm for 30 minutes to see if I could clear the pop. Here is a video of the motor running at 2800. Perfectly smooth. Also a recording of the exhaust at the same time. https://www.dropbox.com/s/6knqqt6ljw7m6ik/20161221_164859.mp4?dl=0 https://www.dropbox.com/s/wpus6yyef07wv9h/spitfire%206.mp3?dl=0 (may have to copy the above links) I attached a picture of the plugs prior to the 2800 run. left to right 1 through 4. Last question. I am running an HIF4 SU. Normally these are in pairs. Since I am running a single, would the standard needle be correct for this setup. I need to get the car on a gas analyser to see if it is running lean. The car does seem to improve the richer I adjust the HIF4. Just wondering if I should go with a richer needle?  |
| Bruce Cunha |
| I also took the belt off the air pump and ran the engine. No change in the pop. |
| Bruce Cunha |
| Plug gap on no.2 looks wider than the others and that brownish shiney look on a couple of the centre insulators needs cleaning off- your pop could be coming from there, specially no2 with the wider gap as well With the SU What did it come off- IF the carb came off a car with a similar sized engine to yours but as half of a twin set--- On your engine it will run rich in general What method have you used to adjust your idle mixture |
| William Revit |
| Bruce, As Willy asked above, and I asked earlier can you tell us a little more about the HIF-4 carburetor you have installed on the engine. Is it new, or re-built unit, and do you know what needle and jet you have installed? I found my old Haynes SU manual, and it looks like the midget/Spitfire 1500's in the UK were equipped with dual HS-4's. Not many engines of this size ran a single HIF (that I could find). The Vanden Plas 1500 (1975) used a single HS-6? Joe Curto (NY/NY) may be the most knowledgable on the subject of SU's (here in the States), and may be able to offer a suggestion as to how best re-jet for the best results. Here's a link; http://joecurto.com/ Regards, Larry C. |
| Larry C '74 B/GT |
| None of your links work for me, a different error message (or just a blank screen with the last one) for each. "I could not detect any pops interspersed with the rhythmic thump of the non-firing cylinder." Are you saying that while you had each cylinder disabled there were no pops in the exhaust (in addition to the regular beat of the non-firing cylinder) at all? That seem's, well, unlikely. I can't see a regular 1/32" difference in a valve lift causing an intermittent miss-fire. "Tried the timing light on the valve. Could not get it to freeze the valve." Didn't explain fully. It won't freeze the valves for the cylinder you have the pick-up clipped to. If you clip it on each plug lead in turn, and try turning the dial from one extreme to the other, you should find one or more valves somewhere else that it freezes. Has the flicking tach stopped i.e. is the only symptom now the intermittent pop in the exhaust? Just idling or running on the throttle there shouldn't be enough unburnt fuel in the exhaust to cause the sort of popping you get on the overrun that you might get with an exhaust leak, or with an air-pump if the gulp valve has failed. Have you done the bigger/smaller plug gaps yet? You should. If you can't hear a change in the beat at the plug or the inlet or exhaust manifold then you my be chasing a will-o'-the-wisp. In my experience from when these engines were current you would be very lucky not to get an occasional change in exhaust note. The crux of the matter is, can you see or feel anything when driving the car? If not, then leave it be. |
| paulh4 |
| Paul, Sorry about the links mate, but I also have problems from time to time with links from the UK, or Australia. Try a copy/paste for them , and see if that helps? Regards, Larry C. http://joecurto.com/ |
| Larry C '74 B/GT |
| Bruce, I would think with all you have done, there would be some improvement form your original problem. Can you disable all the smog stuff and then test the engine.?? At least note if there is any difference in performance. Another try would be take the car out for a good long run 50-75 miles and see if that "blows out" some "gunk" that may have formed over the idled years. Cheers Gary 79 MGB |
| gary hansen |
| Really appreciate all the input. I get very little on the triumph site in the US. Ok. HIF 4 was purchased from a person who ran it as a single carb on a similar 1500 spitfire. Only item that he changed was that the stud holes need to be enlarged. Otherwise it matches the manifold perfectly. I have not identified the needle size yet, but that is going to happen tomorrow. Carb has not been rebuilt, but I did set the float. It is near exactly to factory specs. Jet moves up and down smootly and there is no corrosion, discoloration on the piston or the jet needle. Bowl is clean. float jet is clean, passages are clean. With the better meter, there is no deflection with the pop. I also used the meter to check the resistance on the spark plug wires (4000 ohms for the plug wires and 5000 for the coil lead), The meter also checks cylinder balance (grounding the positive lead and touching the negative lead to a spring attached to each spark plug and measured on the high ohm meter). There was no significant difference in the readings. Point resistance shows good on the meter. I did unhook the belt to the smog pump. No change. I also have disconnected the EGR. No change. I found my colortune and put it on the motor (another tool I forgot I had). I noted I could not get a yellow flame at idle, even with the carb jet at max richness the best I can see is light blue. When I quickly accelerate the motor, I do get the Blue/Yellow/blue color. I also note an occasional bright yellow burst in the colortune. I could not coordinate this with the pop but it may be when the pop occurs. It does appear that the pop gets less the more rich I make the carb (well past the max rpm gain point). I am wondering if using a single HIF4 may require it to be a richer needle? I have read that a lean motor can cause a miss. I know this sounds confusing given I cant hear any pop or change in the cylinders or at the exhaust ports. I also took the car for a drive (risky as it does not have any license plates). I would drive this car in a heartbeat. Very peppy, great pickup, and quick. I do note when I let off the gas, I get backfire out the exhaust. Paul. Will adjust the gap smaller and larger tomorrow. Also, thanks for the clarification on the strobe. Try this link for the motor video and sound recording. https://goo.gl/photos/8LWD8ufFYBxmNFwA8 Sure is an exercise in system checking. Frustrating, but I am learning more. |
| Bruce Cunha |
| Try this link for the sound recording at 2800 rpm. https://drive.google.com/open?id=0B7hHzLnm12qETnlJZXhKcnFET3M Unsure what I am doing wrong with the link posting. None seem to be coming across as a url clickable link |
| Bruce Cunha |
| Bruce, when you post a link, for some reason the computer systems seem to change http to https. All you need to do to make the link work is delete that unnecessary s. Mike |
| Mike Howlett |
| Bruce, I've had a look and listen to your posts and the "pop" you are getting sounds to me like it is exhaust related. Has the exhaust system been checked and in particular the catalytic converter if it has one fitted? Found this on the web - "Symptoms of a faulty cat are the build up and release of pressure in the exhaust system that acts almost as a capacitor. This reflects back toward the engine and causes a hesitation and miss in the RPM range. The symptoms become more pronounced if the exhaust system has been made free flowing when a performance exhaust system is installed, mimicking a ignition miss or backfire". Maybe worth a look? Andy |
| Andy Robinson |
| Andy Usually when a cat has a problem top end performance is off which apparently isn;t the case here----but as they say never say never Bruce If the cat is unboltable off the manifold it could well be worth a try to loosen it off and let the manifold blow to atmosphere for a try I'm off for a few days and will check back in early next week to see how you have progressed Very interested to know what needle is in that carb and why it won't richen up to get a good idle mixture You could try sliding a couple of fingers across the front of it at idle to choke it a bit to see if you can get a result A car with a cat idles leaner than a car without, to keep the cat healthy, that's why the air pump is there to make the cat think the engine is running lean I would think the idle mixture should be around 2% co without the air operating Till then Have a nice Christmas guys willy |
| William Revit |
| Larry - thanks but it's been Bruce's links I could not get any results from, and they were copied and pasted. However the new ones and the old ones are working today. FWIW when I post a link here it doesn't add an 's' to the 'http', and if I delete the s in the browser address bar Dropbox puts it back in again. But that's by-the-by. Given the limitations of computer audio that does seem to be an explosion in the exhaust to me as well. If that is happening when you are videoing at the engine, I can't see any engine rock either, which also tends to confirm it's not a combustion chamber problem. The backfire on lift-off further confirms it is an exhaust problem, maybe the gulp valve isn't doing what it is supposed to. As to not being able to get a rich mixture, needles vary very little at the first two stations which is about where it should be idling, so I would suspect something else. A lean mixture gives a 'splashy' exhaust, whereas on my computer your audio is definitely more of a pop as you say, it reminds me of a old agricultural single-cylinder stationary engine where the governor has a similar effect. There again, if you can richen past the point of max rpm, and especially if you start to get the rythmic 'drrr, drrr, drrr' of grossly rich, the mixture range does seem to be OK. As an HIF does this have a manual choke? Can't tell from the video knowing very little about the Spitfire. If so, what effect does gradually pulling that have on the Colortune and the pop? |
| paulh4 |
| If you get the "pop" when backing off the gas, it would appear that you have a leak in the exhaust system. Also, a Colortune doesn't respond very well to unleaded fuels. If the EGR valve was playing up, the engine wouldn't idle below 2,000 rpms. RAY |
| rjm RAY |
| Did not get to try the different spark plug gap change today. I did find that the HIF4 has an AAU needle in it. I note that Moss has an ABD needle for this carb. Will that run richer toward idle? Worth a try? Could not find a number on the HIF. It does have a manual choke. Pretty easy to disconnect the cat from the exhaust manifold. Any issues (other than noise) in running the car straight off the manifold? I am trying to find a place that has a gas analyser, this could help me set the carbs and tell me how it will go at smog. I did get a chance to look at the cat when I replaced the exhaust manifold gasket. You can look right down into the cat on the spitfire. The honeycomb is perfect. No holes or visible cracks. Color is a silver color. Not saying that it is still good. After the rich mixture that the ZS carb was putting through it, it very well could be bad. I have felt for leaks around the two exhaust pipe flanges and have not felt anything leaking out, but can look a bit closer at the exhaust system. Ray. I seem to remember that the color tune was not as good now with unleaded fuel. I tried it just to see what I would see. Wonder why no one has updated the color chart for today's fuel" Again, Thanks for all the advice. This is a frustrating issue. Too nice a car to not get it on the road.  |
| Bruce Cunha |
| "Too nice a car to not get it on the road." Looks it, apart from those god-awful lumps on the front bumper! They look twice as big as the MGB equivalents. |
| paulh4 |
| Agree completely Paul. Thank goodness UK Triumphs didn't have to wear those awful things. |
| Mike Howlett |
| Casual reading on this Christmas Eve waiting for Father Christmas. A bit off topic from Bruce's original 'miss" problem, but here's a bit of background on the NSTA's reasoning for the early 1970's bumpers. Surprising how many US cars couldn't pass the test even after several upgrades. I for one liked the MGB solution given the circumstances at the time. The Midget and Spitfire not so much. http://www.iihs.org/externaldata/srdata/docs/sr0620.pdf Merry Christmas, Larry C. |
| Larry C '74 B/GT |
| There is a link on the Burlen SU site to the minty lamb site which shows the needle diameter s for all the needles. It also has a. Compare facility that will show the differences between AAU and ABD Happy Christmas |
| Michael Beswick |
| Thanks Michael. That is an interesting page. Using the check box "comparison" it looks like the ABD only is different at station 4 and 5. So it does not look like it would address my issue. http://www.mintylamb.co.uk/suneedle/ Going to put some more time on the exhaust to look for a leak today. I think disconnecting the manifold from the cat will give a better picture. As for the bumpers. A lot of folks convert over to chrome. If it were mine, I might, but then, it is also important to have some "original" cars. |
| Bruce Cunha |
| Regarding the front bumper protrusions, when those came out I overheard some teen boys commenting cars like that now had "breasts." Actually they used a different term, but it always stuck in my head and that is how I think of it still today, and the bigger the better as pops always said. And those special bumpers is the reason why the bonnet has not been dented up front from parking lot or parallel parking mishaps over the years. |
| S Cole |
| Bruce, A good way to look for exhaust system leaks is to have someone plug the tail pipe with a rag while you look and listen for the leak. If the system is tight, the person holding the rag should let off now and then to temper the amount of back pressure generated. Charley |
| C R Huff |
| Probably well known but I might as well mention it ... They were also known as 'Sabrina' bumpers, after a certain actress of the period. |
| paulh4 |
| Paul, It seems Sabrina was also famous for Bell & Howell Colour Slide Projectors adverts.  |
| Larry C '74 B/GT |
| You could put an eye out with that. Ok, todays work. Put a vacuum cleaner on blow onto the tailpipe. Pressurizing the exhaust. That way I was able to use soapy water to check for leaks without the exhaust getting hot. Also checked the gulp valve and it was sealing just fine. Did find a small leak in the donught just past the catalytic converter. So now I am very comfortable there are no leaks. Pop is still there. Fiddled with the carb. Noted that the pop does get more frequent when you move lean on the carb adjustment. Going rich lessens the pop, but I run out of adjustment prior to it going away. Called Joe Curto in NY. At his suggestion, I ordered an AAA and an AAM needle. Found a shop close to the house that has a gas analyser. Once I try the new needles, I will take it in to adjust the carb using the analyser. |
| Bruce Cunha |
| Bruce I'm sure your guy with the exhaust sniffer will guide you but just in case---- Depending on the efficiency of your cat you will probably need to get into the exhaust somewhere before the cat to get a reading Loosen the cat off and get in there or up in where the gulp valve is maybe---anywhere you can get a true reading not affected by the cat willy |
| William Revit |
| "You could put an eye out with that" Two, if you were lucky. If you can't richen it enough to stop the pop (sounds like a game-show) by adjusting the jet then I'll be surprised if needles will make the difference, especially at idle. They only have microscopic differences one to another. Also popping like you have would be very common with a weak mixture. Just saying, you might as well try them. I'd also be taking all the emissions stuff off and try to get back to basics as well, rather than just disabling it but leaving it attached. |
| paulh4 |
| Did you try sliding a couple of fingers over the face of the carb at idle to choke it a bit to see if pop went away------------- |
| William Revit |
| Thanks Paul. It is sounding more and more like a lean miss. Understand that there is not a lot of difference with the new needles but for the little cost, worth a try. I understand that in the UK Triumph had a 1500 sedan that ran a single HS4 SU. Any potential you might be able to find what needle they used in that? William. Yep, have slowly closed off the carb inlet. It does not change the pop, but it does increase the RPM. The gas analyzer will tell me where we are. The shop I found had a Jag out front, a 72 Spitfire with a Weber on the rack, and a TR250 in the back bay that they are getting running. They are not a British Car shop specifically, but it does look like they may be able to help. |
| Bruce Cunha |
| Bruce, Triumph did make two 1500 Saloons (Sedans), the earlier one was the Toledo and the latter one was the Dolomite. Both of these models used Twin HS4 Carbs. Early models of the Toledo and the Dolomite used ABT needles. The later Dolomite used ADN needles. See info from the Burlen website: http://sucarb.co.uk/cf/vehicle/list/?manufacturer=Triumph&vehicle=Dolomite Andy |
| Andy Robinson |
| "have slowly closed off the carb inlet. It does not change the pop, but it does increase the RPM." That implies it's still not rich enough when not closed off. However you said earlier that you can richen by moving the jet past the point of maximum idle rpm. Those two situations do not equate. Either the jet is not lowering as one would expect, or you have a very weird needle that gets thicker again past a certain point. These are HIFs you have, and not HSs, yes? I suggested earlier pulling the choke and seeing what effect that had, both on the pop and to confirm that you could make it grossly rich as a test. |
| paulh4 |
| Bruce, that carburetor was jetted so that it would run very lean to pass US and CA smog requirements. When Moss modified the HIF44 carburetor, for use with their supercharger system, they went with a BCA needle. RAY |
| rjm RAY |
| Yep I would think Co should be about 2% upstream of the cat for a carby car with a cat with the air pump hose disconnected and blocked (for adjusting ) Unless Triumph has a different method --some makers devise some strange idle mixture setting procedures to enable them to comply with the regs of the day- An early non cat car for example would/should be around 5%co but this would be too rich for a cat car and end up killing the cat without lots of air being pumped into the exhaust before the cat A later fuel injected cat equipped car usually gets under 1%----------A carby equipped car would idle very erratically this lean I've just read right back through all this and there are a couple of things that hit me-- Ignition timing-you have it on 10deg-fair enough BUT What is the spec for your car---? A lot of manufacturers at that time were running a lot less advance than that which would allow them to wind the throttle open more and run leaner mixtures to get past emisions testing----- a possibility Also Being a different carby to what was on the car originally could there be a difference in where or what quantity of engine breather air is getting into the inlet causing an overlean situation Willy |
| William Revit |
| Willy, Not sure if this is correct for Bruce's California Spit, but should be close enough for basic settings. Bruce, Still waiting for a few snap's of the engine bay? Lazza  |
| Larry C '74 B/GT |
| Cheers Lazza I havn't gotten too involved in this as we don't know if this is a California spec car or not or what equipment it has For example the California car has a vac retard on the dizzy where normally there would be a vac advance Changing the carby causes all sorts of problems if it is a Cal. spec car as the SU won't have the vac port for vac retard to work properly If it's hooked up to a normal vac advance port on an SU by mistake or misadventure the timing will retard as it comes off idle instead of staying stable until under load---- There are that many possibles without seeing the car it's almost impossible to help Some good pics of the carby , distributor , plumbing etc would help but there aren't any so------- I'm just hoping the guys with the gas analyser are on top of their game to help Bruce get it sorted My current thought is that the car is supposed to have vac retard at idle and that that isn't hooked up because of the SU causing a over advance situation at idle The vac retard would pull the timing back to a few deg.after tdc and more throttle would be needed for good idle speed and I suspect that would get rid of the popping-----------maybe willy |
| William Revit |
| "For example the California car has a vac retard on the dizzy where normally there would be a vac advance" I don't know about Triumphs but MGBs moved the vacuum take-off from the carb to the inlet manifold (1971 for North American spec, 1977 for other markets), but it was still vacuum advance in that advance increased proportionally with vacuum. The only difference is that manifold vacuum gives full vacuum advance at idle, whereas carb vacuum gives none. But as soon as the accelerator starts opening by the tiniest amount carb vacuum very rapidly rises to become the same as manifold vacuum, and as the throttle is opened further both fall gradually towards zero. To all intents and purposes in any driving mode both manifold and carb give exactly the same signal to the engine. |
| paulh4 |
| Paul-------yes But from what I understand the 79-80 Californian Triumph had a vac retard system like the old Mercedes used to have The timing would be set to spec but with the vac retard on the correct vac port on the carb they idle on full retard, right back behind tdc and as the throttle opens the vac drops off and ignition gets advanced up from this retarded position All good, but I just noticed in Bruce's first posting that he has a 25D in it It would still be interesting to retard it back and see what happens--just out of interest cheers willy |
| William Revit |
| The US spec TR6 used a combination vacuum advance/retard unit.I've also seen this dual unit on quite a few other imported cars from that era, as well as on US cars. RAY |
| rjm RAY |
| Ok, looks like I need to post more information (and pictures). Car is a Federal Smog. Not a CA smog. I was at the owners house today and found a folder with all the registration and also the full maintenance history. Car was brought into CA in 1996. Has smogged in 96,98,2000, 2002. Sold to the owner in 2004. Specifications on the car are the ones Larry posted. HIF4 did not have a vacuum port and the Spitfire does not have any setup for a manifold vacuum. We found some threads on line on how to add the port. It goes on the bottom of the carb as the HIF throttle works backwards. Car has all the smog system in place and are working. Air pump pushes air through a one way gulp valve to the bottom of the exhaust manifold, just above the Catalytic converter. Carb has a vacuum hose that pulls vapors out of the valve cover, and also operates the charcoal canister system for the gas tank and the float bowl vapor recovery. EGR runs off the carb vacuum and starts opening just as acceleration starts. This also runs the vacuum advance on the distributor. Since the 25D is from an early B (67), which also runs off a ported vacuum, I would think it would be working correctly.  |
| Bruce Cunha |
| Sorry, last post had some errors. Car was brought into California in 1989. It passed smog in 89,91,93, 95, 97, 99, 2001. Was sold to this owner in 2003 and has been in his garage since. Car was purchased by the second owner in 1993, Maintenance record I found noted the car "backfires" and was"running rich" in 1993 with 35,600 miles. Carb was rebuilt and a new Catalytic Converter was put in. A new muffler and tail pipe put on in 1993 with 37,800 miles. I also show they replaced the exhaust manifold. Clutch was slipping at 39,200 due to a leaking rear seal. Clutch was replaced along with the seal. Car now has 55,555 miles, so 20,000 on the cat. ,  |
| Bruce Cunha |
| It is somewhat concerning that it needed all this work at 35 to 40 thousand miles, but it was build in 1978. Looks like backfire and running rich is not unusual for this car. But it did smog 7 times. For those in CA. I know part of the smog is a visual inspection and the SU is not original. This would fail the visual. I took it to a local smog shop to get a preliminary and the shop owner did not know the difference between an SU and a ZS carb. Only issue he had was his picture for the CA charcoal setup was different. I pointed out this was a federal car and showed him that the setup was correct for the federal car. Other than that, no issues with anything. So I am crossing my fingers it passes the three gas analysis and he passes it.  |
| Bruce Cunha |
| In talking to the owner, we convinced him that this is not the car for he and his wife to drive now. He is in his mid 70's and she is 69. While I would normally not dissuade someone from a british car. These are not folks that I would put in this car. No real good British shops in the area, and he is not a mechanic. He does have a 49 MG YT, that I am working on getting on the road. Beautiful car just setting in his garage. He does not want to part with it yet and I want him to be able to drive it a few more times as his health is failing. I am hoping this car ends up as mine in the future.  |
| Bruce Cunha |
The original distributor in this spitfire had a vacuum advance that also was ported off the carb. It came off the top of the ZS just ahead of the throttle. This picture shows the SU with the vacuum line marked. |
| Bruce Cunha |
| Paul. To clarify. I setup the HIF per the factory instructions with the jet at 0.060 down from the bridge. Then enrich the carb until the RPM is at max. The RPM keep going up until I reach the end of the jet adjustment. I put my fingers below the throttle opening and slowly slide them up the opening. The RPM continue to go up until I hit just about half way and then the engine dies. Interesting that the Salon's use needles that are much leaner than the AAU. I should have the new needles in tomorrow, so that will tell me if they help eliminate the pop. It does look like the AAA should make it run richer. Here is the ZS carb with vacuum port.  |
| Bruce Cunha |
| Just a thought - is there excessive play in the carburettor butterfly shaft/bushes to make it run lean at idle? Test with carby cleaner aerosol spray pack or an unlit propane torch (be careful!). Or you could go all out with a Redline Smoke Pro! http://redlinedetection.com/products/smoke-pro-total-tech Mike |
| Mike Ellsmore |
| BTW us Aussie MGA boys have a special attraction to Sabrina! https://youtu.be/8XjDqIG7jvA |
| Mike Ellsmore |
| Bruce I'm thinking you are going in the right direction trying the new needle if sticking to the SU With the ZS carb, did you pull the top off to check the dashpot diaphram,as they do split, and stop the piston lifting which in turn makes them run rich OR- If someone has had it apart and not lined the notch on the diaphram up with the housing notch will also cause richness--or the diaphram not fitted to the piston corectly Good luck with the needle willy As far as how your setup is at the moment, All looks connected corectly for that dizzy Happy New Year guys |
| William Revit |
| Bruce, Good start on the photo's, but still a few questions. First, can you take a few more with the air cleaner removed? Second, I can't tell from the photo's you posted if you have a secondary absorption canister in your system, equipped with the anti-run-on valve, or how all of this is piped? Happy New Year, Larry C.  |
| Larry C '74 B/GT |
| Will have a few pictures without the Air Cleaner tomorrow. Got the needles in from Joe Curto today, so will be playing with these. Larry. Federal has two canisters. First canister is pretty much a pre filter. That is, air comes in, goes through the charcoal out the bottom and into the first can which is under vacuum and also collects from the fuel tank and the float bowl. See the picture in the 31 December 2016 at 04:46:54 post. I rebuild both canisters with new filters and new charcoal. The CA smog also has two canisters with an electronic valve coming off the canister ( not a clue what it does) and also uses both canisters in the system. Here is the Federal smog system. http://www.triumphspitfire.com/images/emissions/78emissions.jpg Here is the CA smog system. As for the ZS. Carb was rebuild by myself with a new kit. It was also rebuild by a British Car shop in Sacramento. I also got a donor carb to replace the water choke. Neither of us could get the carb to stop running rich. It was the British car shop that recommended going with the HIF4.  |
| Bruce Cunha |
| Bruce While I think of it-- With the vac. advance teed into the egr vac. hose, It will work fine but, 'sometimes' when they are hooked together like that, there 'can' be a situation where the vac. stored in the egr chamber at cruising speed is enough to hold the advance on too much if the throttle is suddenly opened causing a ping To fix it you need a restrictor with just a tiny pin hole in it in the 'y'piece end of the egr connector tube The egr action will be a bit more relaxed but that won't matter Best place to get a restrictor is to take the tube to the local craft shop and get into their little metal beads--You'll be spoilt for choices, it's like going to a lolly shop It may not need doing but thought I'd spit it out while I thought of it Cheers willy |
| William Revit |
| Bruce, I think the device you are referring to between the canisters might be the anti-run-on valve. Seen in this diagram as (#6). Willy, Good suggestion, but not sure I follow with the "EGR" restrictor. Which leg of the "Y" should he place this, or does it matter? (Lolly Shop = Candy Store. Lazza  |
| Larry C '74 B/GT |
| "I think the device you are referring to between the canisters might be the anti-run-on valve" Almost certainly. When the ignition is switched off with a running engine the valve operates to allow manifold vacuum to such the fuel out of the carb jets, which is what effectively stops the engine (and not the ignition on late model MGBs for example which is due to a wiring design error). It operates from a normally closed contact on the ignition switch i.e. closed when the ignition is off, and a normally open oil pressure switch which closes with oil pressure. When the valve has stopped the engine, and oil pressure dies away, the latter switch releases the valve. The second canister (on MGBs at least) was an addition to the large hose on the bottom of the valve to trap fumes from the manifold vacuum line which could otherwise escape to atmosphere. All that plumbing can cause problems, so it might be an idea to disconnect that pipe from the manifold and plug the port, as well as the those on the carb overflows but leave those open, EGR, gulp valve, air injection etc. |
| paulh4 |
| Larry Hi The small vac hose starts at the port on the carb and goes out to the 'Y' piece where it splits with one hose going to the EGR and the other to the dizzy The restrictor needs to be in the start of the EGR hose just after the 'Y' piece This allows the vac. advance to respond normally without being affected by the vac buildup in the EGR Again I stress, this might not need doing, but if it pings a bit when first opening the throttle it could help prevent that from happening Happy New Year willy |
| William Revit |
| My SU bible shows Triumph 1500's in various forms running on single HS4's with needles AAK or ABD, the AAK is weaker than AAU, as indeed is MOSS'S ABG. The ABD does however have a slightly richer stage at 4,5 and 6. but is otherwise the same as your AAU. Baar in mind all these needles are identical at the first station. |
| Allan Reeling |
| Going to work on the spitfire today and change the needles. I see the various stations with the needle charts. How do the stations relate to the position of the jet? That is, manual says the jet should be around 0.06 below the bridge. So does position 1 correlate to the jet level with the bridge or? It must be an interesting process to see how they taper these. |
| Bruce Cunha |
Here are some shots of the carb without the air cleaner.
 |
| Bruce Cunha |
Another (don't know why, but the pictures are rotating when loading)
 |
| Bruce Cunha |
| one more of the other side. Also. All restrictors are in place for the vacuum system. I know there is vacuum to the vacuum advance when past idle as I can feel vacuum on the line. I will measure that also.  |
| Bruce Cunha |
| I've seen drawings that show the stations starting immediately below the lower shoulder, and statements that 1 and 2 are for idle. But bearing mind the piston is slightly raised at idle, and the jet is below the bridge, the stations may well start lower. Really one would need to measure a needle with a micrometer and compare to the charts. I have a couple of old BBUs from my V8 and a dial gauge. The first station on that is said to be .990, but mine immediately below the lower shoulder are .970, and taper down to the stated .680 right at the tip. Implying the first station is right at the top, so at idle one could be in station 2 or 3 if the stations are a regular 3mm apart. But as I've said before I think needle profile a red herring. The first station is common to virtually all needles, the second only 10 thou slimmer on a few, and only then do you start to get significant differences. If you can't make the mixture grossly rich by winding the jet all the way down, there is something else wrong. Out of interest, using a depth gauge, just what is the range of the jet adjustment i.e. how much above to how much below? You have said that when moving the jet down the revs keep going up until you run out of adjustment, but then using your fingers you can progressively close the carb inlet and the revs keep going up until you reach half-way when it dies. That implies either a very significant vacuum leak somewhere, or very significant fuel starvation. |
| paulh4 |
| Bruce, Any measurement relating to bridge and jet is only a starting point for setting the carb up. Given that you have a needle which is 'close", The jet is then adjusted to give the best idle, or fast idle, using the throttle stop screw, which is what I do. Also remember these needles are tapered, the stage measurements are there to give you a comparison. Where the needle finishes up in relation to the jet is dependent on lots of variables within the engine and, of course, your desired tick over speed. |
| Allan Reeling |
| Bruce, Thanks for the updated photo's. No problem with the orientation I was able to turn and enlarge them when down loaded. Helpful when not familiar with an engine type. Not sure if the 1500 Spitfires (UK) with dual SU's were equipped from the factory with insulation blocks between the carburetors and intake manifold (or a heat shield), but I think all MGB's & (modern) Midgets had them. More for vaporization (lock) is my understanding, but one of my first thoughts looking at your photo. http://sucarb.co.uk/insulating-manifold-air-inlet-gaskets/insulating-gaskets/om-insulation-block.html Regards, Lazza |
| Larry C '74 B/GT |
| The only other thing I can think off regarding the needle is to check that it isn't gunged up making it thicker, or the jet narrower, which would cause starvation. And regardless of blocking the intake making the revs rise, it it doesn't also stop the popping then you have more than one problem. |
| paulh4 |
| hundred crikey |
| William Revit |
| I have a customer who regularly turns up complaining her Midget 1500 is not running well and sure enough, I get in it and it has a misfire. I take it out on one of the quiet straight local country roads and floor the throttle - after half a dozen runs up and down the mile or so of road, the car is running perfectly. My advice is stop fiddling and give the car a good hard run - then see if the pop is still there. |
| Chris at Octarine Services |
| Thanks all. Did not get to install the new jet/jets today, but will get on it tomorrow. Chris. I would love to do just that, and I do feel running it would help. With all the tuning and checking we have done, I figure the motor has 6 hours of run time on it since I started it. I have run it at 2800 rpm for nearly 30 minutes. No difference/ Unfortunately it does not have a current registration or even plates, so taking it out on the road is a risk. If this car did not need to pass smog here in California, I would drive it in a heartbeat. Paul. That is some of the reasons I am very frustrated with this car. Something is just not right and I have yet to figure it out. Changing the jet will at least give me more information I hate to self doubt my abilities, but I have not been able to identify any vacuum leak to any spot on this car where there might be a potential for a leak. Now remember, this car has a designed vacuum leak in that the charcoal canisters are open to the atmosphere and under vacuum from the carb. My concern on a vacuum leak is that the miss is so inconsistent. I would think it would be more regular with a leak. Larry. The original ZS did not have any spacer between the carb and the manifold. Understand your thinking as my MG's all have spacers. |
| Bruce Cunha |
| Bruce, Another thought concerning the connection from the crankcase breather (valve cover), and charcoal canister/s (via "T" connection) to the carburetor on the Spitfire engine. Now that you've switched to the SU carburetor, have you tried running the engine with only the purge line from the crankcase breather (similar to the MGB) connected to the carburetor to eliminate the "designed" vacuum leak from the canister? Lazza  |
| Larry C '74 B/GT |
| May sound crazy, but it worked on my 79 B. Check the tightness of the nuts that attach the manifolds to the cylinder head. Mine were loose enough to create a vacuum leak. I know you mentioned spraying around the mating surfaces. I did the same, checking for leaks, but I suppose the spray evaporated before it made contact with the mating surfaces. Nothing to lose here. Cheers Gary 79 MGB |
| gary hansen |
| Bruce, just to pick up on Gary's point, it looks like there has been a known problem with 1500 Spitfires and clearance issues between the inlet and exhaust manifolds, See this website http://www.triumphspitfire.com/Manifold.html The website talks about a massive vacuum leak being caused, but I guess a small leak could also occur, depending on how bad the problem is. Worth a look if you are checking the manifold nuts. Andy |
| Andy Robinson |
| Larry. Of note. If I plug off the intake to the charcoal canister, the car dies. ( I think the increase in vacuum causes the float bowl to pull up and shut off the fuel). I can try plugging the vacuum line off the carb and see what it does. Gary and Andy. I though this to be the problem when I noted one of the bottom bolts on the exhaust/intake manifold was missing along with the keeper. Took the manifolds of and put on a new payon gasket. Made a tool to get in to the two lower bolts (talk about bad engineering, it is near impossible to get these tight. No way to torque them) I am reasonably certain I have everything correct and tight. I use a straw on the starting fluid can to check the lower part of the manifold for leaks. Not finding any. |
| Bruce Cunha |
| Bruce, Sorry, I should have stated to leave the top canister connection to the carburetor open to atmosphere for the test. The idea was to eliminate that connection from the SU carburetor. I think what Gary and Andy were suggesting was to double check the tightness again. Lazza |
| Lawrence Cordeiro |
| First, I really want to thank all that have assisted with this issue. I have gotten more help from this group than any of the threads I have posted on the US triumph site. I worked on the Spitfire today. It had a seal leak on the water pump, so first item was to replace it. I mentioned that the engineering for the lower manifold bolts really sucked. One of the hardest bolts I have ever had to get to. Can't figure how they torqued these at the factory. Doubt they did. ( I did recheck and the nuts are tight and no leak I can detect) So given that, the water pump was probably the easiest and best engineered pump I have replaced. No hoses to remove, just three nuts that are easy to get to and the impeller/pulley section of the pump pulls out. It literally took about 10 minutes to change the pump. Next was to recheck vacuum lines. I started by plugging the charcoal canister. Car's RPM increases with the ports on the second canister plugged. I then took the line off to the float bowl. No change. Plug the line and the car dies. Not sure why, perhaps it builds pressure in the float chamber and closes the fuel needle valve? Ok, now the good news. Put the AAA needle in the HIF. After a call to Joe Curto to figure out the correct orientation of the floating needle collar (the scribed line on bottom of the collar goes towards the butterfly) and setting the jet to 0.60 off the bridge, I started the car. Still was popping, so adjusted the jet towards rich until the RPM maxed out. Slight turn towards lean and the car is running the best it has. Exhaust temp is very low, CO levels per my hand held meter are the lowest I have achieved yet. The pop is very slight to not noticeable. First is the recording with the AAU.(https://www.dropbox.com/s/wpus6yyef07wv9h/spitfire%206.mp3?dl=0 ) Next is the recording today with the AAA. I had the phone a bit closer and the sound is a bit raspy (https://www.dropbox.com/s/ekddr26e961ajx4/spitfire%207.mp3?dl=0 ) There is still a slight pop when letting off the throttle after a quick acceleration, so I probably need a bit more tuning. Car will go to the shop next week to get on a gas analyzer. This will allow me to really fine tune the carb to get it hopefully within limits for smog. I am also noticing a bit of clicky/clacky noise coming out of the air pump. It is pumping air fine, but not sure if the noise is normal. I will take a recording of it and post it. |
| Bruce Cunha |
| Bruce All you have to do now is get your hands on that Y Type Well done Enjoy the drive willy |
| William Revit |
| Just something that may be worth checking as regards the "lift off pop". 1) The poundage of the piston spring. It's easy to check with a piece of folded card and some sensitive scales, most of the 1500 Triumphs used a red spring, but the marking paint diapers very soon in the spring's life. They are 4.5 oz /1.53" springs, i.e., when put on scales and compressed to 1.53" the scales should read 4.5oz.; and 2) That the piston is free to rise and fall, and falls fully, hitting the venturi bridge as it bottoms. Check it without the damper. 3) Check that the damper has been assembled correctly. Pushing the damper in to an oil filled piston should meet reasonable resistance, pulling it out much less. |
| Allan Reeling |
| "the charcoal canisters are open to the atmosphere" That's why I suggest disconnecting all the emissions kit and plugging any ports they use. The crankcase breathing on the MGB (at least) uses the carb to draw air through the crankcase, then the rocker cover, then the canister. The rocker cover has a restrictor to limit the flow and create a small depression inside the engine, which is detectable by a change in the engine idle as you remove and replace the (sealed) oil filler cap. The canister filters the air, as it purges the charcoal granules, and draws in fresh air. If you block the fresh-air inlet then the vacuum is applied to the float chamber overflow/breather ports, which are also connected to the canister, which sucks the fuel out and stops the engine. This is basically what the anti-runon valve does. Allan's No.2 (if you'll pardon the expression): The piston should indeed fall smartly when released and hit the bridge with a click with the damper removed, but it is essential that it does exactly the same thing with the damper fitted. If it does not then the damper piston is faulty in some way. If you can now adjust the jet between obviously weak and obviously rich, then that is a great step forwards. |
| paulh4 |
| http://www.dropbox.com/s/wpus6yyef07wv9h/spitfire%206.mp3?dl=0 http://www.dropbox.com/s/ekddr26e961ajx4/spitfire%207.mp3?dl=0 |
| 1 Paper |
| Well what a fun project this was I dont like drop box and wont install it on the new phone so im at a disdvantage My thought and was suggested by several due to the simplistity of these engine... remove everything to just the basic engine and plug everything off maybe 2 -3 hours work and replace the cat with a straight pipe take out the wiring off the gauges coil ect ect hot wire to the pos of battery...move the fuel pump as close to carbs as you can with a piece of new fuel hose make it just the engine and the oil pressure/water temp then hook up a vacume gauge If it does or does not miss at that point it wont take long to trace it down If you still get a pop ... then its none of the externals like the admissions ...disconnect fuel hose and watch that the flow from the pump dosnt hicup for several minutes ...id then go tonthe electeic with new jumper wires and connections and take the old out of play... then id test the carb If rhe stripped down bare bones engine has no miss... then you know the problem is in one of the assecories thats added on ...keep adding parts till you get rhe miss back Realistically about a day to find this if your motivated This is not exactly a 2007 porsha where talking about...these cars arw barly more then a garden tractor |
| 1 Paper |
| Btw.... what happened with the sticking exhaust valve broken sping Theory and did you pull the push rods and check for bends and pull the lifters to see if cracked is the rocker assembly worn or sticking from oil varnish from sitting so long Have you pulled the sump pan to see if any metal shavings in the pan...then check inside the block far any aftermarket replacement bolts making slight contact with enterniol moving parts when the block flexes at higher rpms I think after 45 days you have been at this its time to bite the bullet and strip this engine down to its lowest common denominator that it still can run with as little on the engine as possiable and check for the miss fire...and go from there other wise your just fighting your own brain ...something im very good at Prop |
| 1 Paper |
| Ok, interesting that Dropbox adds the "S" after HTTP. I will change this next time. If the time on the gas analyser does not work, Taking everything off and adding one part at a time is pretty much my only option. As pointed out, a day's work. William. I did get the tires inflated last week on the YT. So, as soon as the rains stop here, I will be able to roll it out of the garage, and start the work to get it going. I am hoping it will not be anything like what the spitfire was/is. |
| Bruce Cunha |
| You said the dissy was replaced...with what? How was the dissy recurved and who did the recurving and was the specialist given all the correct info do they know about the carberation change and account for that when they set the dissy curve on the new dissy Hhhmmm any chance you found a decent used dissy on ebay and just stuck it in the engine without a rebuild and having it recurved to fit the engine Who ever rebuilt and recurved the dissy could they have not set up the curve correctly or rebuolt it incorrectly or may not have understood the specs ...maybe the curve is not set to california dissy specs but to non california specs Or maaybe the specialist got confused and set the curve to an mg midget and not an mgb... you can use the 45D dissy ON an high performance mg midget You mentikned your using points and condensors ... do you know for a fact the condensor is funtioning perferctly... how did you test that? Its not leaking juice is it... And NO WOBBLE or PLAY in the dissy shaft ... you have checked that ... the guy that rebuilt it didnt go ro lunch and for get to replace the seal when he came back to finish rwbuolding and recurving the new dissy in this engine Prop |
| 1 Paper |
| Sorry to hang up on the dissy But you said you replaced the dissy and that was it... nothing more and on that topic and no one else asked anything further from what i read Dissys are not universial plug and play from one engine to the next Do you know if the dissy came from the exact same year make modle and assory package as this car... i mean the exact same car as your working on... no this one had AC And the other that the dissy had came with AC as qn example P |
| 1 Paper |
| Bruce I'm a bit of a sucker for Y types A mate has one for his daily driver, it's a bit of a modified one with 3500Rover and auto, disc brakes etc A fine chariot I have a shortened YA chassis that I'm building a special on---------------one day Most of the YT's went to the US and Aust, they are a bit of a rarity in the UK What condition is your friend's car in- willy Better than mine I hope  |
| William Revit |
| Willy Haha ... did the trialer come free with the. Car or did you have to pay extra Prop |
| 1 Paper |
| Sloppy throttle shafts at the bushings will do that. Also seen when all appears nice and tight, but the technician doing the bushings reamed all the way through the (inside) carb body. |
| S Cole |
| Bruce, the rain isn't going to stop anytime soon. RAY |
| rjm RAY |
| Their are rubber seals on the throttle shafts of the HIF's. |
| Lawrence Cordeiro |
| s cole yep I've seen that where the body has been machined right through but the bushes havn't been pushed right through properly leaving a gap at each side of the butterfly---good call, I hadn't remembered that till you mentioned it Might be worth checking Bruce---if it's been bushed-- Larry you are correct in saying there are seals but this is air leaking around the edge of the butterfly itself through the little gap where the tunnel has been machined right through willy |
| William Revit |
| In that case it is what it is. Most likely what it is is worn shafts and the air is getting in past the shaft. |
| S Cole |
| "air leaking around the edge of the butterfly itself" That will pull mixture through, and causes a high idle even with the idle screw(s) backed right off, rather than a vacuum leak. |
| paulh4 |
| Sloppy shaft will allow excess air in through the shaft and/or through the disaffected butterfly in a random way that can be quite confounding. Depending on which way the shaft wiggles it may take a gasp of air now and then through the shaft bore or/and also cause random misalignment that causes the butterfly not to shut or open normally, or not close all the way. Can cause uneven idle and also makes the carbs hard or impossible to tune. |
| S Cole |
This thread was discussed between 15/12/2016 and 15/01/2017
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