I have a 1500 cm Yamaha 4wheeler/dual range. My problem is that i was dragging a piece of wood in reverse when my high range forward and reverse locked together. I can use the low range with no problems but it will not move in high range or reverse. Also, It will not idle. I have adjusted the main jet, cleaned the carb in and out and replaced/gapped the plug. NGK plug.

 

If you feel clever enough, you can open up the case. It could be a bent shift fork, or something more expensive. I'd probably take it to the dealer and get it fixed. I guess you meant a 500 cc model. A 1500 cc ATV would be pretty scary. As far as idle, take out the pilot jet and blow it out. Screw in the PMS screw all the way, then back out a turn. Once you get it idling you can turn it out to the highest rpm, then turn in a bit. Main jet only controls 3/4 throttle and up.

 

Thanks for the info