'01 426- Been riding for a year, never been rebuilt, ran great. In Jan put the 450 Cam in it, made a huge diff. For the past couple of months, the throttle has begun to get more and more finicky. When your on the gas, it runs, when your just holding the throttle, it doesnt know whether to keep running, or die, like its hesitating or trying to cut out. Very, Very rough, not even rideable.. This has been a problem that has slowly come on, getting progressively worse. I decided to go ahead and rebuild the top end. New piston, wrist pin, rings, and timing chain. Got everything back together, but has a couple of issues with timing using a new chain without any stretching. Found out I was 1 tooth off on the exhaust cam, adjusted, and it fired. Yook it to the track, and still had the throttle problems. It will run when you hold the throttle open and the engine is under load, but after the engine is up to speed, or it is maintaining speed, it doesnt know where to cut out, or keep running. Going back to the timing problem, I tore it down again, and checked the timing, now the Intake cam was way retarded, beyond what 450 Cam Mod PDF shows, so thinking I was once again off, I notched the intake cam back one and it looked to be perfect. Put it all back together, and tried to ride it, and now its even worse, completely unridable, it sputtered and was cutting out soo bad, I only got into 2 turns on the track. Things I have checked- Valve Clearance- All within Spec Carb Jets- Main 160 Pilot 42 - AZ 1200ft Re-Packed Muffler New Plug Air Filter Clean No Exhaust dents or dings Items to consider- Cleaning Entire Carb Checking Ehaust Manifold to Head Leakage Timing (AGAIN!!!!) I am at a complete loss. It never used to run this way. The only things I have adjust was the Pilot Jet and Main Jet when I went to the mountains. The bike has not undergone any serious crashes. We thought the performance problem might have been due to a worn piston, but now that it has been replaced, and the problem still exists, I am at a loss. It was a problem that grew progressively, and wasnt due to me changing anything out, or making any changes to the bike.... My fellow moto mechs/Buddies, seem to think its in the timing, but the problem existed prior to even starting the rebuild... HELP!!!