We just bought a 94 kingquad and it has some problems with it. First it smokes like a 2 stroke, and barely idles and stalls out a lot, i think this may be because the person who had it before us didnt rejet the carb when he added a cobra exhaust and k&n airfilter, am i right? It also smokes around the engine head, the smoke smells like oil. The guy said he had the engine rebuilt at a polaris dealer. what could be the reason for this?