well i got a 421 cheetah cub with 35mm pwk's, p/d cool head with 22cc domes, T5's, stock reeds, +4 timing, and 115 long rod.my jetting is at 170 mains and 58 pilots with air screw 1 an 1/2 turns out. at sea level. i ran my bike in pismo this weekend and blew my right piston. my nickelsill looked good and had NO nail catchers. the only thing wrong was a thin film of aluminum left behind by the piston. at the time i was running the bike on 87 pump fuel. i know it was a DUMB ASS IDEA!!! but i changed both pistons out there. then i used a 50 50 mix of 87 and C12 race fuel. now it backfires in first gear when i punch it.and the rest of the gears have power but its not all there. im still running lean and have tried bumping up on the mains but its not making a difference. i need help. and if you have a similar set up can you tell me what jetting your running and your elevation. and what you think of my gas mixture. all advice will be greatly APPRECIATED! THANKS