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MG MGB Technical - Desperate, engine missing, stalling

Twice over the last year, my 67 MGB mk1 has, after driving for a period of time, and in traffic, the engine starts spluttering and missing, nearly as if the distributor was wet or something like that or starved for fuel. It only did it two unrelated times, the last where the car actually stopped and wouldn't start again. I was convinced we would have to get a tow so we went and had some lunch and relaxed for about an hour and came back to the car and it started ! Drove off thinking all was ok and it was just one of those things and after about 15mins it started to splutter and miss again, but this time after about 2 minutes whatever it was seemed to clear it self and we drove home (about an hour) without further problem. That was about 4 months ago and never had a problem again so I just put it down to dirty fuel or something. Anyway, it happenned the other day and I had to get the car towed to my mechanic. He played around with a few things and changed the plugs and points but couldn't really identify any direct problem.He said the carbys were really dirty, and cleaned them best he could but he suggested I may need to get them done by an SU specialist. ANyway, I got the car back and have been driving it for two days without incident...until tonight. Did the same bloody thing again and wouldn't start. Again I left it for 2 hours and started and drove perfectly ?
I am really lost as to where to even start looking. It could be some intermittent fuel blockage or something but something tells me it is something to do with the ignition. Is it possible the coil or something is breaking down once it gets warm, or hot ?
Everytime this problem happens has when I have been on an extende drive or in traffic, and I leave it for an hour or two and the problem seems to go away.
ANy help greatly appreciated, really don't know what to do?
Craig

Yes, the coil could be breaking down. On a '67, though, I would first check float bowl levels when it acts up. '67s didn't have any inline fuel filters and can easily get trash in the float bowls, along with the old rust in the gas tank problem. An inline filter after a good carb cleaning may just solve your problem.
Ken Lessig

Craig
Did you change the condenser as well as the points, you problem sounds like a classic case of a condenser failing then recovering after a cooling down period.
Worth changing it just to see if it is, it's a lot cheaper than rebuilding the carbs.

Colin
C J Bryan

Start at the cheap end:
Rotor arm
Condenser
HT leads
Dizzy cap
Coil
You said you have new plugs and points

another possibility - do you have surpressor on the coil? I once had a metro that was totally dead because the surpressor had gone and was taking all the power out of the lt circuit to the coil.

good luck
Richard
Richard Bacon

Craig,This sounds like a common problem with older SU fuel pumps. The points start to arc and can fail in the open position shutting down fuel to the carbs. When it cools down the pump comes back to life. Next time that it happens, disconnect the fuel line going into the rear carb, turn the ignition to on and see how much, if any, gas it pumps out. If little or none, at least you have isolated the fuel pump as beeing good or bad. Ray
RAY

Craig - Your problem could definitely be the SU fuel pump as stated by Ray, or it could be your gas cap. There is a vent in the gas cap to relieve the vacuum formed int he tank as gas is drawn out of it. If this vent gets clogged and quits venting the tank, a vacuum is formed and the car starts sputtering and quits. After the car sits for awhile, the vacuum finally goes away, the car starts and acts like nothing is wrong. A good indication that this is the problem is if the problem is more frequent right after filling the tank. The next time you experience the problem, pull the side of the road and remove the gas cap. If you hear, eve a very faint whoosh of air venting into the tank, that is your problem. If this fails to solve the problem, then follow Ray's instruction and if no fuel is coming through, smack the pump with a convenient weapon (not one of mass destruction though)and see if the pumps starts up again. If it does, then it's time to rebuild or replace the pump. Cheers - Dave
David DuBois

Craig, Next time your car won't start you must eliminate either ingition or fuel systems. Fuel is easiest and done by having a look in a carburettor bowl to see if there is fuel in it. If there is then move on to the ignition, fit a condenser and if you can borrow a coil from another car then so much the better. My guess is that the bowl will be empty so you can point the finger directly at the fuel pump.
Iain MacKintosh

This thread was discussed between 31/03/2004 and 01/04/2004

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