I'm curious what causes a backfire? My bike lets out a kaboom periodically at high rpm that will scare the crap out of you. I think the problem is the taiwanese muffler doesn't fit very well to the header pipe so air can enter the muffler. At a RPM under certain conditions the air enters the exhaust and ignites in a loud boom.
My prospective fix is to cut a piece of sheet copper into a strip and wrap it around the muffler flange so the ring clamp that seats the muffler to header pipe seats better and tightens down. I guess a taiwanese 1 3/4" is different than an american one.
That's one possible cause. IIRC your Buell is a single. If your bike has a 'waste spark' ignition (and it probably does), it will fire the plug on the compression and the exhaust stroke. If there's any residual unburned fuel in the exhaust and the exhaust valve is still slightly open, blammo!
I'll look into the wasted spark hypothesis, the bike has wasted oil and wasted gas so why not wasted spark. Thanks for the suggestion Jensen, I'll see if sealing the exhaust better fixes the problem. I was going to use exhaust paste but I seem to remove/repair my exhaust once every few months so I don't want to remove the whole mess if I don't have to.
