my 2000 zr 600 won't go over 65mph. i put a new belts on and it still does the same thing. the tack is at 8000rpm and bounces back and fourth like a rev limiter and it also back fires when i try staying in the throttle. i just rebuilt the top end w new pistons and rings. it has a clutch kit and engages at 5 grand which i though seemed high. i was thinking it was maybe something in the primary clutch. i bought it w a blown motor so i dont know what it ran like before i got it running. anyone have any ideas on what to do or what it could be.