1 of the things that causes backfiring is running a rich a/f mixture. basicly unburnt fuel goes in the exhaust manfold where it explodes.
another cause is no cat, which muffles small pops and little backfires which you normally dont hear.
another is running a venting bov on a car with a sesnative afm. dunno about the lines but on my turbo laser, a vented bov made it back fire like nutz cause the computer would measure the air coming, and add the fuel needed, but this air would leave the bov so the a/f mixture would go rich, therfore cuasing a backfire.
i thinks thats all right
steve