Lion wrote on 12/31/69 at 16:00:05:I have the same problem: it still backfires after changing the main jet, white spacer mod, pod air filter, platinum spark plug. So you mean changing the muffler to a bigger flower one will stop backfiring?
Intake, fuel, spark and exhaust. If you up grade the fuel system, then you have to increase intake of air, better spark and elimination of exhaust. My mods were K&N drop in, iridium plug, 1/3 spacer and a slash cut sportster muffler. My backfire was because I was leaking air coming in and exhaust coming out. It created a backfire when I accelerated from 2nd to 3rd. I regained a balance and the bike seems fine. I still sometimes get a very small fart when I shut down, but its usually after I have been pulling hard on the throttle. Funny how you can suffer from lean and rich conditions with the same bike. Just last week I was crusing the long way home and had a little throtle fun, got my 2nd to 3rd backfire then when I pulled into the gargae and shut the bike off I got a little fart from the exhaust. Sounded like my wife blowing out a candle.