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MG MGB Technical - Engine Sputtering When Under Load

What is the most likely cause for engine (MGB 3-Main)sputter when under load? I have checked the carbs for fuel starvation, but this doesn't appear to be the problem. I tested each carb float bowl/float assy. by first removing the float bowl covers and checking fuel flow. There appears to be sufficient fuel passing through the needle assy when open and the fuel flow stops when the float bowl cover is turned upside down. I also cleaned the passageway from the float bowl to the carb's jets after removing the piston and needle assy. I could be wrong, but I don't think it is a fuel problem. If it is an electrical problem, what is the most likely cause? Coil??? Note the dwell and plug gaps are per spec.

Any suggestions will be appreciated
Frank Grimaldi

I had a simular problem last year. After much trouble shooting around the fuel delivery system, I finaly discoverd that the ignition timing was much too far advanced. Good luck. -Benrie
B.H. Hall

hi frank
just had this happen to me. thought it was carbs and read on here that most ( carb problems ) are electrical problems . it was the condensor, replaced with a new one and was exactly the same. bought another and solved problem. even new one was no good. apparently they are crap nowadays. hope this solves your problem.

bob.
Bob Taylor

I agree that it is most likely to be an ignition problem. Too advanced timing or a bad condenser as suggested, or perhaps a very worn distributor. But there are other and more strange possibilities.

My 3 main MGB had a tendency to sputter when going uphill. I read somewhere on this BBS that a loose baffle in a silencer could cause this, but I guess I did not really believe it. But when I replaced the front silencer with a small straight through "bomb" type to get more ground clearance, the sputter disappeared!

Tore
Tore

A simple check for fuel delivery problems is to switch off the ignition when it starts sputtering, coast to a halt, then when everything is quiet turn on the ignition again. If the pump (assuming it is the factory SU type) either doesn't click at all or only makes one click, then it isn't a fuel problem. Another check is to remove the fuel pipe from a carb (be aware of a spurt of fuel if the ignition has been on recently), direct it into a comntainer, and turn on the ignition. It should deliver at least one Imperial pint per minute, in practice near double that, in a steady stream of pulses with negligible bubbles. If both those tests are OK it is almost certainly ignition.
Paul Hunt

Problem Solved !!!

I thank everyone for their suggestions. After reading the the different possibilities, I felt confident that the problem was a faulty condenser. While in process of changing the condenser, I noticed that the ground wire from the base plate to the distributor's body had come unsoldered. I resoldered it, and went ahead and replaced the condenser with a used, but a known to be good, condenser. Car runs great.
Frank Grimaldi

It's surprising how essential that ground wire is even though the points plate has a sliding contact as well. Many years ago I had a Scimitar GTE with a Ford 3-litre engine and the distributor for that had no ground wire. It gave me a couple of heart-stopping moments of spluttering when pulling out into traffic, until I read a recommendation in the owners club mag to fit an earth wire, after which it was fine. This problem is more likely with manifold vacuum as the points plate moves from full vacuum advance to zero when you open the accelerator.
Paul Hunt

This thread was discussed between 23/04/2009 and 26/04/2009

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