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MG MGB Technical - Finally attempting a start
| After 12 years I am now (hopefully) ready for a start. I have fuel at the carb, starter turning freely, oil pressure on cranking, new plugs with proper gap, and a spark at each lead. The motor has coughed a few times (just long enough to spit the starter pinion off the ring gear. I have choke on, throttle open. Should I be considering some assistance - over here we have a spray product called "Start Ya B^$#@!d" designed for starting stubborn engines or engines coming back from a layoff. Anyone had experience with this or similar products? Any notes of caution? I don't want to have reached this stage only to stuff things uop! John |
| John Minchin |
| Coolant in?! Battery really really charged up? I'd just try it with the usual precautions and maybe easy access to the battery terminal which could be whipped off in the event of something nasty happening! If it won't start then recheck timing and carbs. Easy Start could help but it will then mask the cause of non starting. I tend to associate ES with trying to start under very damp conditions (bit like the UK at the moment!) |
| Michael Beswick |
| Michael Yes, sorry - engine flushed and coolant in, battery charged, new coil, leads, etc. I have a battery cutoff switch too. As for damp conditions, it wasn't too bad here today, but the next few days will be damp and down to 11 degrees max(C). Timing - I did check this and double checked then decided the distributor drive shaft was not aligned properly. I will triple check that the No1 plug is firing on the compression stroke and not the exhaust!! John |
| John Minchin |
| Oh, and I forgot to ask, what does a good strong spark look like?? The coil is new but "unbranded" so that might be a problem if the spark is weak? John |
| John Minchin |
| "I have choke on, throttle open" If the above means what I think it means (foot on the throttle, holding it open), put your foot under the seat. The throttle should only be open the amount that the choke linkage holds it for starting. Cheers - Dave |
| David DuBois |
| Dave makes a good point! Coils usually fail when hot and I can't describe a "good" spark. Though if you have a pal who has a working coil + points car you could have a look to compare. Most "branded" stuff seems to emanate from some dodgy places now, so the one you have is just as likely to be good! (And it is already fitted!) Just a thought-if it doesn't start quickly, remember the choke will soon cause the plugs to be wet, so either push it in or stop and dry the plugs. Avoid the temptation to thump the throttle and most of our cars tend to like good choke to start but then need the choke pushing in to about half way. Only trial and error will determine yours but the above seems common. Good Luck |
| Michael Beswick |
| Thanks for the heads up on throttle and choke. As for the coil, it did get very hot oner day when I left the ignition on for a long while when testing wires and continuity, voltage drops etc It was too hot to touch - could it be cooked? Yesterday when attempting a start, it was warm after a period of trying - but not what i'd call hot John |
| John Minchin |
| John, 'Too hot to touch', depending on the duration, is probably not good for a coil. The fact the motor has coughed a few times suggests the starting sequence is being completed, but it may be with low charge from the above. In that case I'd borrow a known good coil and swap it in. That is a simple task and will offer an opportunity to assess the fitness of your existing, providing you do get a start. Regards Roger |
| Roger T |
| As Dave said about the choke. We used to tell customers to put it in neutral, pull the choke all the way out with both hands, turn to lock, get out of the car, reach in and turn the key. If it didn't start then it was our (Mechanics) fault. Are you certain the valves are adjusted correctly? Low compression on one cylinder will make it kick the starter out but quit running when the next cylinder comes up. Same if you have the plug leads mixed up. It takes two cylinders in a row firing to get running. FRM |
| FR Millmore |
| Are you sure that you have the ignition timed to fire just as the points are opening and not just as they are closing. Remember that the distributor shaft turns anti clockwise so the points should just be starting to open as the cam lobe approaches the points heel from below. If you have it timed just as they are closing which is a common mistake that is no good. |
| Iain MacKintosh |
| Firing order? 1 3 4 2 anti-clockwise? An MGB shouldn't need any fancy starting fluids, it if doesn't start something is wrong. What are the plugs like after cranking a while - wet? Smell strongly of fuel? Or nothing? First is flooded, third is no fuel. For flooding on a car that normally starts push the choke in and floor the throttle and crank again, getting ready to release the throttle and half pull the choke, but in this case it could be no sparks and a lot of cranking with a lot of choke. If it coughs a couple of times try pushing the choke in, opening the throttle and kep cranking for a bit longer. The spark should jump a minimum of 1/4 inch, and up to half an inch. If it barely jumps a plug gap the condenser could be faulty or out of circuit. If no spark at all then there you go. You can overheat a coil by leaving the ignition on, to the point that it won't start, but unless you are unlucky it shouldn't permanently damage the coil unless left on for hours, flattening the battery. |
| PaulH Solihull |
| Find a photo of the distributor and plug side of the engine and make sure you have the plug wires connected to the correct plugs and terminals. Try a different setting of the choke each time you attempt a start. -G. |
| Glenn G |
| John, these engines start easily after a long layoff as long as timing and spark are ok. and you have oil pressure. Yours sounds ready to go. Just make sure you don't have a vacuum leak at the intake manifold, ie PVC valve or other connection. The tell tale is backfiring. |
| Barc Cunningham |
| John as the boys said no throttle just full choke. It does however help to put your foot on the throttle as you pull the choke as it takes the load off the choke mechanism, then remove your foot to start. Start you "Ba" is a Neulon product which are usually pretty good. Good luck with it. Denis |
| Denis4 |
| Sorry, I have to dispute the no throttle theory :<) An MGB may start cold with full choke and no throttle, but I don't believe that is necessary, and I don't think it is the best way to start one. I have been cold starting my '73 B since new in June of 1973 with full choke and a little throttle and it has always started easily for 39 years and 170,000 miles. Always. In sub zero temps in the early days when it was my daily driver to 100+°F. I have started my '57 MGA since 2003 that way also, with never a problem. (The choke linkages are adjusted properly and the fast idle cams work correctly, so I am not overcoming other problems with the throttle) Sometimes a single odd fire can mean not enough fuel or not rich enough. As mentioned above, I would pull some spark plugs immediately after some starting attempts and see if they are damp with fuel. If they are, it is more likely ignition or timing related. Ralph |
| L Poupard |
| Well, spark is at least 6mm (1/4"), I pulled the plugs and they were wet with fuel. Wires are connected correctly to plugs - however I will double check the timing to make sure everything is set with No1 on compression stroke and not exhaust by mistake. Also noticed the vacuum advance line is cracked where the small bulb attaches to it. It will need fixing or replacing, but I guess for now I could just blank it off at the manifold? It is so miserable and cold today (max about 10 C (50F)) Psychologically, I didnt feel like giving it another try. As soon as the sun comes out! |
| John Minchin |
| "full choke and a little throttle" A little throttle isn't going to hurt anything on a cold start, much less prevent it starting. The point is it shouldn't be needed. I've been starting BL cars with SU carbs since the late 60s and if things are adjusted correctly it should start without any throttle. Hot start with no throttle does often need a little throttle until it catches, if for no other reason than to blip the revs high enough to start the alternator charging. ECU equipped cars do that by design. A vacuum leak on the advance pipe will weaken either the rear carb or cylinders either side of the manifold connection. Shouldn't be enough to prevent starting but plug the carb/manifold anyway. You say the 'bulb', do you mean the vacuum capsule on the distributor? Or the bulge in the metal line? I thought the latter was only used on carb vacuum cars. |
| PaulH Solihull |
| Paul The vacuum pipe assembly 163-640 - has a metal bulb or capsule in the line - presumably to even out vacuum levels so the distributor doesn't get too excited. Joint between bulb and pipe is cracked. As far as I know this part is required on my early Mk1 - ref Clausager photo of iris blue car. Sun still not showing itself - too cold for me to start let alone the car! John |
| John Minchin |
| That bulb is a vapour separator to stop fuel getting into the vacuum capsule and rotting the diaphragm, was only used on earlier cars, which took the vacuum from the rear carb not the manifold. It shouldn't be needed as the carb port is on top of the throat, presumably it came off another application and was dropped later on. However it *is* needed on V8s as the port is on the bottom. After my second capsule failed I fabricated my own chamber. |
| PaulH Solihull |
| Is it going John ?? |
| William Revit |
| Not yet William I can assure you that you won't need to read about it here first, you will hear me from your place! Paul Clausage shows the vac line with bulb on 69 and earlier cars. After that they seem to be plain bulbless lines. Mine does come from the carb as shown.You can see the cracvked paint where the tube has disconnected from the bulb. John  |
| John Minchin |
| Hey William, did you hear me - IT STARTED!!!!!! First I triple checked the static timing - was OK. Then, I stripped down the dashpot covers and pistons - they were binding and wouldn't lift! Cleaned everything up and reassembled - then away she went. Next problem - it wanted to go full throttle so I had to turn it off straight away. (Luckily I had oil pressure up because of the cranking) Throttle cable was free and movable andle throttle shaft rotating. Something must be wrong at the carb but not sure what. Any ideas where to start? John |
| John Minchin |
| Felt the ground shake but didn't twig onto what it was- As it was hard to start then revved hard maybee you have a giant air leak -- brake booster hose diconnected ??? Also have a look at the blanking plugs on either end of the balance tube of the inlet manifold, I've seen them blown out before - rare but it happens Got caught with one a while back, it was the back one that you can't see -- have a feel Willy Also check that both throttle shafts are returning right back--- If the balance is way out one carby can be open instead of shut at idle and you get the big rev thing happening. |
| William Revit |
| Willy I think the starting prob was because both Carb pistons were stuck - couldnt lift up. I will check manifold as you suggest - no brake booster on my ancient Mk1 so that couldnt be leaking :-) Also I will need to check that butterflies can actually close when pedal is released and not being held open all the time somehow. John |
| John Minchin |
| Hope I dont insult anyone... Did you try starting fluid? Will start with the choke off. You might not be getting full travel on the choke cable. She should start up regarless... Then check your timing. |
| JRB Mr |
| It cannot be a vacuum leak! An engine will only run if it has fuel getting into the cylinders, which normally has to come through the carbs. For it to race at full throttle the throttle butterflies have to be open a significant amount, or missing (!), or there is some other route for fuel to get into the cylinders. |
| PaulH Solihull |
| Well, the butterflies are both still open when the throttle cable is loose - perhaps 5mm gap at the bottom and top of the discs. I guess this is why the engine is revving Now to figure ouit how to ensure they are fully closed. From reading archive, I should also ensure throttle cable is completely free and adjusted with stops adjusted. Also to check that the throttle shafts and connecting piece are freely rotating and not binding. Could the idle screws be completely out of adjustment(bearing in mind this is the first time I have started the engine and who knows what the DPO has done (I've assumed things have been done properly but have still had to redo brakes, starter motor, oil filter assembly, master cylinders, and so on. BTW in the archive from some time ago Ken Rich described similar behaviours (high revving on first start after rebuild) Are there some references easier to follow than the manual (ie with more pictures and diagrams) - apart from Pauln H's site which is very good John |
| John Minchin |
| John, Let me see! After 12 years she has started but "it wanted to go full throttle". 1 Carb pistons "were binding and wouldn't lift!" 2 "the butterflies are both still open when the throttle cable is loose - perhaps 5mm gap at the bottom and top of the discs" 3 "Could the idle screws be completely out of adjustment(bearing in mind this is the first time I have started the engine and who knows what the DPO has done (I've assumed things have been done properly but have still had to redo brakes, starter motor, oil filter assembly, master cylinders, and so on." ???? Time for a carb rebuild/resetup? From what you say, it is probably the only system left you have not already rebuilt! You know it makes sense. regards Roger |
| Roger T |
| You may have to take the carbs off to squint through them to check the butterflies are fully closed with the cables disconnected, interconnecting shaft clamp screws loose, and idle and fast idle screws backed right off. Any of those being wrong can cause one or both butterflies to be open. If they are still open, then the could be jamming in the throat, check they are the right way up, various butterflies have a notch on the edge for a port of one kind or another, or the throttle spindles could be binding in the bushes. |
| PaulH Solihull |
| Roger I think I will try to reset carbs as I've already done, the floats and needles, new fuel lines, new choke cables and attachments. It is clear by inspection that the jets and needles, jets, butterflies are new, and there doesn't appear to be any slop in the shafts. Paul, I started at the beginning - butterflies were being held 1/4 open because the throttle stop was incorrectly set. I unclamped the connecting rod, slackened off the throttle cable and the springs fully closed the butterflies. They seemed quite free, with no binding. Idle and fast idle screws backed right off also. Engine started, but still wanted to race as soon as the throttle butterflies started to open. (I had someone operating them while I cranked). So if the issue is excess air getting in, where else from? - there are some screws and plugs in the manifold but all are tight and have fibre washers so I don't think much air could enter there. There was some backfiring out of the carbs - why?? If it isnt a case of too much air, could it be too much fuel? (hence backfiring?) Is the next step to reset jets to maximum uppermost position and then back off the recommended turns and go from there? Or have I missed something? John |
| John Minchin |
| Hey John I've probably asked before but can;t remember Where abouts in Tassy are you |
| William Revit |
| Float levels ??????????? |
| William Revit |
| Willy I'm in Hobart (Howrah) Float levels - I spent a while setting these - I suppose they still could be too high, and if jets too low then too much fuel flow?? John |
| John Minchin |
| I'm up north so not much use to you really-- Maybee David Short in Hobart could sort you out if you can't get the result you're after - He knows his stuff Willy I don't think your problem is too much fuel .it's sounds more like an actual throttle problem as in the throttle linkages arn't adjusted up properly or it's lean too little fuel or too much air Usually if it's too rich they tend to be docile and there would be the telltale sooty black exhaust Are the jets centerd up nicely so that the dashpot pistons move freely you can test them by removing the dampers from the top of the dashpots and then lift the piston right up with your finger in the mouth of the carb and then lower it down. it should land with a definate clunk and you should be able to raise it again without any sticking or resistance if it is sticky at the bottom at all the jets need to be centred up---- |
| William Revit |
| Willy I do see david quite often - he groans when I appear! I was intending to talk to him about this but wanted to have a bit more of a go to see if it is something simple Would too little fuel cause the backfiring? Still sounds like I should adjust the jets and needles - centring seems OK as pistons drop with a clunk. Unfortunately it hasn't run long enough to get good exhaust colour :-( John |
| John Minchin |
| The return springs (3?) are present and properly mounted ie stretched so they will draw? |
| Roger T |
| Whilst a vacuum leak *will* result in a higher idle for a given throttle opening, it's only slightly higher as the more air that gets in the weaker the mixture gets which eventually makes it idle slower again as well as badly, and eventually will stall. Normally to race the butterflies would be open enough to allow sufficient fuel and air though to allow it to race. If yours are only open far enough to give idling, then fuel/air must be getting past them somehow. How are you setting the idle screws if the engine hasn't run properly yet? You should be able to unscrew them until the engine stalls, because the butterflies are fully closed or almost so. For the engine to run at all with the idle screws backed right off then fuel/air mix is getting past them somehow. The reason the engine *does* speed up with a vacuum leak is that normally at the idle the engine is just a highly inefficient vacuum pump. Let some additional air in, the vacuum reduces, so the 'pump' is doing less work so it runs faster. It's a similar effect to blocking the suction hose (or outlet) on a vacuum cleaner - the motor speeds up. Why? Surely restricting the flow is making it work harder and it should slow down? But with the suction hose blocked no air is flowing through, so the motor is simply whizzing the same air round and round in the fan chamber, i.e. very little 'work', so it speeds up. Like you pedalling a bike when the rear wheel is off the ground. |
| PaulH Solihull |
| OK Roger - springs all present and seem to be working OK - ie throttle shaft now rotates smartly until both butterflies are fully closed. Paul - thanks for the vacuum cleaner analogy - makes it very clear. Both idle screws are backed right off at this stage. My next step is to check all manifold joints have seals and are tight, and also to check the seals on the plugs and screws along the top of the manifold, and to blank off the vacuum line that goes to distributor. I cant think where else I could get a significant leak of air into the manifold. Someone also suggested checking fuel level in the jets is about right, and that there is no flooding of fuel into the intakes. Pretty sure that isnt happening - there are new needle valves in float bowls, no fuel flowing out of overflow pipes, fuel lines connected to the correct pipe on the float bowl lid. I'm assuming that at my next try I should not see over revving, and I should get the engine to stall if I release the throttle. I will report back after the next garage session! John |
| John Minchin |
| Incorrect fuel level in the jets won't cause racing. Fuel wouldn't normally flood up the jets and into the intake, any flooding of the carbs i.e. faulty float valve should overflow out of the vents, although if you have a charcoal canister you can get quite a lot of fuel leaking out before it becomes visible. In either case it would be accompanied by much clicking from the fuel pump - assuming SU. Also you would have to have fuel flooding into the intake *and* a significant vacuum leak before the engine would race - it needs sufficient fuel and air to allow it to do so, not just one of them. BTW new float valves counts for nowt in my book, anything new is suspect if you get problems after fitting it, even if not immediately. |
| PaulH Solihull |
| John Now that you have your butterflies returning right back and moving freely and return springs fitted correctly If it races now with the choke pulled out it will be the adjustment of the fast idle screws that operate off the choke cams that need adjusting back These can be roughly set by getting your assistant to pull the choke choke out while you watch how much the throttle is pulled on - If it looks to pull it on heaps just back the screws off till it only pulls a little throttle on - Usually about 1/4 of the cam should pas the end of the adjusters before contact is made and from there onwards the throttle gets pulled up a bit. The amount of throttle pulled on by the choke is a personal preferance sort of a thing - My view of it is that it only needs to be enough to keep the engine just slightly above normal idle speed at full choke Then after it starts the choke can be crept in as it warms maintaining a fairly normal idle speed till the fully in position is reached The last thing you need is a choke that is adjusted up to do a million revs on a nice cold engine Willy If you're talking to Shorty say g'day from me please,I havn't bumped into him for quite a while cheers |
| William Revit |
| I should change the name of this thread now - to Engine started and running!! After checking and adjusting as per your instructions / advice, I tried again today. Touch of throttle and away she went (choke completely backed off) Sat at a fast idle (2500)and ticked over nicely fro half an hour - about 40-50psi oil, 85(C) temp. No major leaks of funny noises. A few "new part "smells - probably manifold paint, gaskets, etc... Actually drove the car out and up the driveway so I know 1st gearnd the clutch works as well! Now to the fine tuning and adjusting to get things just right. I must say I'm a bit puzzled that it is idling at that speed as the butterflies were fully closed and the idle screws are backed off. But at least it runs. BTW I did check that all manifold gaskets were there and everything was tight (including all the screws and plugs - everything need a tweak up so I'm confident not much air could leak in that way 12 long years to get this far - the end is now in sight! Probably not too soon to thankseveryone for their input and help so far - much appreciated. Willy, I will probably see Davisd later this week so will pass on your greetings. John |
| John Minchin |
| John, How are you determining that the butterflys are actually closed? Charley |
| C R Huff |
| "I'm a bit puzzled that it is idling at that speed as the butterflies were fully closed" Either they are not, or the spindles and bushes are so worn or there is some other problem allowing mixture to get past the closed butterfly. An engine simply cannot run unless it is getting fuel and air in approximately the right quantities, which means it must be getting past (or possibly through if a screw is missing!) the butterflies. If the engine is running reasonably smoothly then it must be getting through or past both of them. Do the butterflies have poppet valves in them? |
| PaulH Solihull |
| Paul, Charley My description did seem rather confusing when I re-read it. What I meant was, with the engine not running, the butterflies appear to be fully closed - I took both dashpot covers off and and pistons out and could see that the springs were rotating them to the closed position. Paul - given your comment about air getting in in sufficient quantities, I suppose I will have to look more closely at just how good the fit is - ie are there any gaps between the disc and the body. There don't appear to be any screws missing, and there are no poppet valves. Not having dismantled or reassembled the butterflies before, is it possible for them to be attached slightly off centre, and hence leave a gap on one side when closed? When I switched off the ignition, there was a small amount of run-on - maybe 3 more "coughs". BTW I must have had a brain freeze when I typed the idle speed - it was a lot less than 2500! - probably only a little faster than the normal range I will investigate further on my next day off John |
| John Minchin |
| John, Yes, it is possible for the butterflies to be attached off center. Also, it is possible to put them in the wrong way around. They have a bevel on their edges that snug up to the bore of the carb. When you put the butterflies in, while the screws are still loose, you flap them open and closed until they find a good "home" and then tighten the screws. Have you made sure the fast idle linkage is not interfering? Have you slacked the clamp that ties the throttle shafts together? Have you looked down the bores with a good light? The first step to synchronizing carbs is to get the butterflies operating together. To do this you back off the stop screws and the fast idle screw. Then slack the clamp between the throttle shafts, get both butterflies fully closed, and carefully bring each stop screw up till they just start to move the butterflies. Then tighten the clamp between the shafts. From here on, to set the idle speed, always turn both throttle screws the same amount. Charley |
| C R Huff |
| "and carefully bring each stop screw up till they just start to move the butterflies" Maybe OK for an initial setting, but the correct way to balance the carbs for air flow is by comparing the 'suck' on each carb either with an airflow meter or listening with a length of hose. The screws will also only balance the carbs at idle, which is relatively unimportant. Far more important is to have them balanced off-idle by opening the throttle slightly and adjusting the interconnecting shaft clamps accordingly. With that balanced then you can adjust the idle screws for balance at idle. |
| PaulH Solihull |
| John, Paul is right. I'm just trying to get you to a point that it runs well enough that you can fine tune it. Charley |
| C R Huff |
| OK, checked again - butterflies look closed but I think are being held open slightly by the idle screws which had been backed off, but not right off. Idle was a bit rough today (not having done anything but inspect since last run) - revs about 800-900. There was a bit of backfiring just as I started to invcrease the revs but once it was idling faster (say 1200) that wasn't evident and the idle was smoother. I suspect the timing is out so I will reset that before doing any more adjusting of carbs. Still only getting 1 water leak from one of the top radiator hose joints - that hose is looking dodgy anyway with some cracks and splits - not good for a hose that has never had hot water or pressure in it. Oil pressure sitting slightly higher today - 50psi at idle One thing that seems good is that it starts first turn of the key (ambient temp about 12C) John |
| John Minchin |
This thread was discussed between 10/05/2012 and 31/05/2012
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