GOOD INSIGHT!!5thTonBench said:If your pairvalve is disabled, then YES pipes leaking at the heads could cause backfire.
It appears the majority of the backfire issues related to pipes deals with the Hardkrome 3 inch straights. It seems to be a gasket issue that resolves this problem.
When I installed my kickers, I looked at the gaskets, they seemed fine and I continued installation. A lot of guys with 3" straights do this, yet after installation find they should have replaced the gaskets.
I am starting to think we should let anyone who is buying them, know that they should spend the extra few bucks and replace gaskets when buying the 3" straights just as a precaution.
The 3" straights must be very particular. The angle that they come in to the heads must be so specific that it becomes a real demand for an absolutely perfect (aka new) gasket. Obviously its pretty darn hard to get any kind of torque wrench in there, but tighten those bolts down good nonetheless (definitely dont kill 'em though). I found it really helped to use ball-ended allen wrenches which let me get into the bolt a lot better.
Good luck, maybe someone here has the part number for the gasket?