MGA mga start and backfire

[dwnuk]

have a 1958 mga and starting has become a problem. Takes a long time to get running and before the engine kicks in it backfires in the tail pipe section. Does this mean my fuel mixture is too lean or too rich? If so what's the best and easiest way to adjust?

Thanks

 

[AndyH]

Backfiring is often caused by a lean mixture. After it's warmed up, try driving with the choke out. Does it still backfire? If not, your mixture's too lean.

 

[jlaird]

Hmm, now I would have thought the other way around. Backfire caused by too much fuel in the pipe.

 

[Steve_S]

Check the mixture and timing.

 

[AndyH]

Actually it can be either rich or lean. With a lean burn, the mixture doesn't get fully combusted in the cyclinder and unburnt fuel enters the exhaust where it ignites. With a rich mixture, the fuel runs out of oxygen and gets passed out. I believe the lean fuel issue is more common on older, carbureted cars. The choke test will tell them apart, if it gets worse you have a rich mixture. Yes and the timing could be off too.

 

[dklawson]

It's also common for lean conditions to cause the backfire to be out the carb(s) instead of the tailpipe.

Always check electrical things first before adjusting the carb(s). Start with a general inspection of the ignition components... plugs, plug wires, dizzy cap and rotor, coil connection.... Once you've replaced any suspect parts dress and reset the points (preferably setting dwell, not gap), then set the ignition timing. With the engine cool, set the valves clearance. If these mechanical and electric settings don't address your problem, then it will be time to consider adjusting the carbs.