I have a question about backfiring. Seems like once all my 12a 7's got over 125k or so they started softly backfiring. It's not a compression or a timing issue. It's actually a carb issue. It happens when I just deccelerate in any gear. I believe it's cause by the carb not mixing correctly at idle. I don't get backfire on quick shifts or if I decelerate with some throttle.

I was just wondering if 13b's also backfire softly like 12a's or if the EFI has significantly improved mixing.

 

Mine dont back fire at all and its a 13b w/o any emisson stuff whats so ever on it ...

 

That's what I am thinking...13b's mix better than the carbs do. My 2nd rotor float runs a little rich. I think the majority of the pops are coming from the excess fuel burning down through the exhaust.

 

My 13B backfires occasionally when I go from acceleration to low throttle, and only under that condition.

My 12A backfired all the time.

 

Usually if the ACV doesn't work right it starts backfiring. Removing it or cleaning it solves the backfiring problem in most cases.

 

With my 12A and Dellorto I only get back firing when decellerating on the off-ramp after I've been driving in 4th gear on the highway at 80+ mph.

Otherwise it's pretty quiet.

 

once my exhaust gets up to temp it will backfire, and i still have a cat... but no ACV