I own a 2001 polaris sportsman 500. Recently it has started to spit and lose power. It only happens after I have been on it between five or ten minutes. If I'm on it in deeper snow, it doesnt even have enough power to turn the wheels. While on the road, it will act up at higher speeds. I discovered the radiator to be completely clogged which I cleaned out, but I dont think this is the cause of the problem. I've heard it could be a sparkplug problem. Please Help!