Watch what you do Bill there seems to be a bunch of way.s to stop the backfire.I was told by a mech. that-go slow with the carb stuff. It depends if you went to an after market muffler.AS I said the bike I bought had a jardine muff when I got it.But it can be fixed by carb work. The bike runs better now then it did. Ill let you know the next step I take. It does not seem to backfire as much.