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General Tech Carbureted TR7 backfiring

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Deictic

Deictic

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Not that I don't enjoy frightening my neighbors to death with gunshot-like sounds, but my two-carb (Stromberg) TR7 backfires frequently after shutting it off. My plugs and plug wires are newer, and I recently timed my distributor with a timing light, so the engine runs very well. I'd appreciate words of wisdom here.
 
The electronic ign may be failing, if it is OE. Make sure the new wires are compatible with the
ignition system metal core wires are a NO NO.
Mad dog
 
Since you say it's loud, I will assume it's backfiring out of the tailpipe rather than the carburetors. Tailpipe backfiring is always...always...ignition related. I would also suspect something in the ignition affecting all cylinders, not just a single plug wire or spark plug. A bad wire or plug will not normally introduce enough raw fuel into the exhaust to cause a backfire. Something is shutting down the ignition, allowing raw fuel to dump into the tailpipe, and then when the ignition comes back it lights off the entire tailpipe at once.

There is one exception, if you are driving aggressively and use the engine to slow the car by downshifting with the throttle at idle...then you may get a tailpipe "popping" as the car slows. This is normally from an air leak in the exhaust system. When spinning fast at idle, carbed engines become very rich. That is normal, due to the high vacuum and fuel being drawn through the carb idle circuit. Normally this rich mixture just blows out of the tailpipe harmlessly. If, however, you have a leak in the exhaust, then the rich mixture becomes combustible and you get "bang....bang, bang...bang" as the car slows in idle.
 
Years ago, I used to have an air-cooled VW that would do that. I found it was because the exhaust valves were too tight. When I adjusted the valve lash correctly, it would go away. You might check it out. ...J.D.
 
So when you turn the key off the engine backfires?????. I cannot see a situation where that would happen. Maybe carbon on the plugs dieseling or the ignition is somehow not turning off right away. but clearly you are igniting unburnt fuel like John mentioned. Do you have an electric fuel pump that pushes fuel back into a hot motor??????

Steve
 
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