QUOTE(914rat @ May 25 2009, 02:33 PM)
Would an exhaust leak cause the backfiring and popping and bucking?
Backfiring on deceleration, yes. Not the popping and bucking though, which sounds more like a clogged low speed jet. Easy enough to check, and much better news than a dropped valve. Did you know these Dellorto's before? I've bought used carburetors with different sized jets. Hell to tune and acts just like a clogged jet until you realize you haven't actually measured every one of them to make sure they're correctly marked and somebody hasn't reamed some of them at some point in a past life.