riding in cooke city this weedend, first day sled ran fine but second day sled was idling really low and had a terrible low end bog and would only rev up to 7000 rpm. had good gas and new plugs. when i pulled the plugs mid day one was brown and the other was gray. also the sled always starts first or second pull but a couple times i didnt think it was going to start, took about ten pulls. what is wrong?. only mod on sled is rumble pack silencer.