I just picked up a Bayou 220, my first ATV, in pretty rough shape. There are lots of issues to work out but the most pressing is that it will not shift into neutral or reverse. What would be the most common causes for this?

The second issue is a distinct lack of power. I can get it going on flat ground, in a straight line but whenever I try to turn the wheel the engine bogs down and sometimes dies. It also dies if I go full throttle. Any suggestions? Thanks!