While you are there, pick up a racing clutch. Well worth the money. If the engine is revving up, it sounds like it is either the slipper or the clutch. It could really be either one. Try tightening your slipper first; that's the easiest thing to do. Do you have the RTR version? If so, it could've just been loose from the factory. Check out the manual and see how to get to it; it isn't hard at all. You need a 10 millimeter open-end wrench, I might add.