Just wanted to let people know what I found with an 2001 engine shuttering at part to full throttle. I did the obvious checks first-cam, timing,coil checks, carb,wiring,plug, etc. The cause of this was as follows: There is a rubber boot that connects the airbox delivery plastic tube to the carb. This boot had gotten soft and each time you cracked the throttle, it would block off the vaccum port going the carb which is used to control the slide. No vacuum-no fuel from the main jet, no upper rpm's. I pulled my hair out trying to find this but kept my cool and finally found it. This might be an isolated case but there are sure alot of people asking about that very problem. The dealers want to go right for the cam due to exhaust lobe issues. Not to say that in many cases this is true but in my case it wouldn't have been. Hope this helps someone from becoming bald. If you think this might be it, just run the bike without the airbox assembly (just for diagnosis purposes) to see if the problem goes away. Good Luck.