i have a 2000 ds 650 that is acting like its hitting a rev limiter. Its random when its doing it you can shut it off and start it right back up and it will rev fine no problems. Its acting like when you put other quads in reverse. any ideas i was thinking some sort of sensor.

 

Try playing with the headlight switch when it does it.. If you have a spare battery, try putting it in. When the battery shorts, it will do something similar to what you are describing.