Same question came up a few weeks ago, this is what I posted in answer to your question.
There is s long hex nut witha lock nut connected to our throttle handle. Loosen the lock nut and turn the long hex nut towards u, keep turning till there is no play left. Be careful of binding, make sure the throttle snaps back fully on its own in all three wheel positions. The lock nut is 10mm and the long hex nut is 8mm. Should be the top line out of the two coming off the throttle handlee. O yea, slide the rubber boot down on the end of the long hex nut.