Originally Posted by 5 speed
I guess I got ahead of myself. I fired it up in the driveway and it ran and idled fine, no backfiring. So I put it together last night (had not gone so far as pulling the tanks) and today it ran terrific, idled perfect, but still backfires when winding down from about 4,000 RPM. .
When a LC8 is perfectly tuned they do this.
It may be possible to tune it out by changing the Air Leak jet on the ACV (air cut valve) it's on the pilot circuit.
If you wish to explore this option I can help further.
If I understand correctly :-
It came back from the shop popping on decel. ..... Spot on.