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MG MGB Technical - Big Bang, a cloud of black smoke

I have been having a bit of trouble with my '70 tourer. It will simply cut out without any warning, sometimes can be restarted immediately at other times it may take anything from 5 to 20 mins, but will always start eventually.
Last evening when driving home, I came to a stop light and was in idle, lights changed and I accelerated, but a huge, i mean huge,(even frightened pedestrians) followed with a large cloud of dense black smoke and carbon, all ove the white car behind me. After the belch, off we went as if nothing had happened, not sure that the white car was happy though.
Can anyone throw a light what may have caused this and do you think the original problem is related?

Regards Ian
I Denton

Ian - you have an air leak in your exhaust system and something (like an over rich situation or one cylinder not firing) is causing unburned fuel to enter the exhaust. Combining the unburned fuel with the air that is entering the exhaust, is causing the Big Bang. Cheers - Dave
David DuBois

Hi Ian
Checked your ign. points lately- Willy
WilliamRevit

What does the tach do when you lose power - while the forward momentum of the car is still spinning the engine? If that has dropped to zero then there is a problem in the ignition LT circuit, and this will cause unburnt fuel put into the exhaust during non-firing cycles to explode when the engine starts firing again.

Whilst an exhaust leak, or a faulty gulp valve, can cause popping on the overrun neither should cause an explosion like that when starting to accelerate. But then again, neither should the cause be an ignition failure as ordinarily waiting at lights that would cause the engine to stop pretty-well instantly.
P Hunt

To me, it sounds as if one carb has a sticking float that is causing it to dump unregulated fuel into the engine. Sometimes it will cause it to stall while other times it will detonate in your exhaust system. By letting it sit for a while, the gas in the engine is evaporating allowing you to restart the engine. Remove the carb lids and inspect them for foriegn matter or wear. RAY
rjm RAY

This thread was discussed on 27/12/2009

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