Had this problem come to me at my shop, what it was the cable was pulling the trottle open to make it rev high, take the cable off an it should ilde normal if it does then you need to adjust the cable either with the 2 nuts on cable they are 12mm or at the pedal, on the pedal, its a stud with a flat spot so you can put a flat head an turn it like your adjusting valves, an losen the nut its a 10mm.. hope this helps Joshua