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MG MGB GT V8 Factory Originals Technical - Minor problem, but still a problem

Every now and then when I really got on the gas pedal and shift between first and second, or second and third, I get a backfire out the tailpipe. It almost never happens any other time except when I'm really on it. Unscientifically, it seems to primarily happen over 4,000 rpm's, but doesn't always happen. It's a bit haphazard. I know my valve springs are brutally strong, and I have a new set, I just haven't taken the time to put them in. Maybe next week I'll get to that.

Any suggestions?

Justin
Justin

Justin,
Check for a small exhaust leak.
Michael S. Domanowski

unburnt fuel - your carb is not closing down the supply as you change gear - maybe the carb acceleration valve or something like a faulty throttle -

Common problem with mechanical fuel injection - when the mixture is much too rich

RW
Roger

I'd check carb settings, but there isn't a carb. It's hotwire fuel injection. =) I like the exhaust idea, I do hear a bit of a ticking noise sometimes (no not from that one debunked lifter).

I'll try to experiment more tonight.
Justin
Justin

Justin,

That ticking may be a leaking exhaust header gasket or small hole/crack in exhaust system near the engine as Mike D suggested.

Pete

1969 MGB 302 V8
PJ Mantell

Can't see it is the carb or FI, why isn't the fuel burning? The spark continues to appear in all cylinders whether the throttle is open or closed. If fuel were still coming through (more than at a rate sufficient for idle) the engine would be racing, but still firing and burning the fuel, even when the throttle is closed.

It *could* be unburnt fuel, but because the spark is failing wehn you lift off the throttle, which can happen if the braided ground wire or the points wire is damaged and going open circuit as the points plate twists under changing vacuum with changing throttle. That is, if you have points ...

On NA emissions MGBs a backfire on lifting off is often caused by a faulty gulp valve.
Paul Hunt

My 2 cents...

Fuel mixture, timing, or valve sticking.
Carl

This thread was discussed between 29/07/2003 and 30/07/2003

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