Engine backfires until warmup when letting off the accelerator pedal.

1984 L69 5 speed.

Possible cause/causes?

Thanks,
Rich

 

Back fire out the exhaust or out the intake?

 

From the driver's seat sounds like exhaust. If I'm very gentle on the throttle lifting off then it is fine. Only happens when cold and during warmup.

 

My experience with back fire from the exhaust is from a lean condition from the carb or a vacuum leak. Unburned gases make there way into the exhaust and then blow up instead in the chambers. Can be hard to nail down a cause, I've even had it from a bad spark plug. I'd start looking at vacuum lines. I'm thinking it's leaning out when you close the throttle valve too quickly.

 

OK. Thank you. I'll look into it. Any of those are possible at this point. Have not had it long enough to look anything over. Vacuum first. Then full tuneup including plugs. Then carb. I'll update this thread as things get done.