I just rebuilt my 2003 kx250 from the ground up almost every nut and bolt and all of the engine (top end, bottom end, complete clutch). it has new radiators and exhaust as well. When i bought the exhaust originally it was racing season and i didn't have the time to re-jet the bike immediately and like an idiot i decided to race it while it was running lean and ended up blowing the motor. so i put in the recommended 165 main jet and 52 pilot jet when i re-built the bike. I finally started the bike yesterday and it started with a few kicks and seemed to run ok. But it smokes like crazy. its insane how much smoke it makes, and I don't want to rev it too much to try to clean it out because its a brand new motor. it doesn't have that characteristic castor 927 premix smell either. I've put like 15 minutes of run time on the motor and it just doesn't seem right. It makes a sound similar to the sound you hear when you slowly push down the kickstart once in a while too if you rev it and that kinda scares me.