I have a 1999 polaris sportsman 500 and just got it back from the shop to check out why it was shifting hard. They said it was a worn belt but, when I took it for a ride it shifted the same as before. I bought a factory repair manual and adjusted the shift linkages and now it shifts great but, when I put in reverse it moves by itself if on level ground. Think the idle is a little high. Any suggestions. If you think the idle is high how do I turn it down? The repair manual doesn't show how to turn it down.