What model is it? If it's a 400 it's either a LTZ400 Quad Sport or an Eiger. They came in 2 or 4wd and foot shift or automatic. Let us know which model you have.
Don't think it's electrical, but I have been wrong once or twice in my life.
Actually, it sounds like you may be running a bit rich and some of the excess fuel is actually burning in the exhaust pipe. The last guy on here with that problem made it better by turning in his idle mixture screw. The idle (pilot) circuit effects fuel mixture for all or part of the lower 2/3's of the rpm range. Check to see what color your spark plug center electrode is. Black is too rich, white is too lean, and tan is just right.
Welcome to the forum.
Last edited by oldeerslayer; 03-28-2013 at 05:18 AM.