Backfire on deceleration?

I had leaks at my header flange to the head, and at the collector junction - car sounded like a herd of hunters on opening day. New gaskets, tightened bolts, now I only get the occasional pop on a super long clutch-out coast.

Lots of other things can cause pops and backfires, but it's 100% imperative that there be no exhaust leaks. Not even a little bit. After that, it's fuel and timing.