Have you been tampering with it or did it just start doing it of it's own accord,check for free-play on the twistgrip you should have some movement before you feel the throttle on,adjust it at the cable end on the twistgrip,if you have had the tank off or messed about the cable may be mis-routed,start it and move the bars from lock to lock if it runs faster or slower your cable is in the wrong position.
Rich, April 2011