fourtrax idle issues

Just bought a 2000 fourtrax 300. It runs great but just about everytime I stop the four wheeler stalls. I've adjusted the idle screw to where it idles great sitting still but it cuts off everytime after I stop running. Another problem I'm having with it is when I rev it in neutral it doesn't come back down to idle. It will rev high until I adjust the choke on the handle bar. Most of these problems seem to be happening at the carb. I just don't know where to begin to look.

thanks