Ok I have a 2010 ktm 300. I put a new topend in it 2 weeks ago and it ran great. I raced a harescramble last weekend and half way through the 2 hour race it stopped hitting powerband. Right at the point the powerband should open up it kinda just flattens out. Just goes blaahhh! I took the carb apart and cleaned jets and everything and still same thing. Any ideas? And PS, the reason I rebuilt topend is it had a rattle/knocking sound and my friend said it was piston slap. And the noise has come back again. I used a vertex piston and rings. I also just took the side cover off to inspect if powervalve is opening at rpm and it is opening. the bike also is hard to start, need to hold throttle wide open almost for it to fire up. And it won't idle, I turned idle adjustment all the way in and it will stall after 30 seconds.