I have a 2001 Arctic cat 500 auto that seems to be running rich. the spark plug is new & gets black & very wet after running. I rejetted it from a 148 to a 140 main jet. And it still blubbers. it wont rev-up. I removed cleaned & inspected the choke plunger twice. Does this machine have a timing advance mechanism? Or is it advanced in the CDI box? Or is there something else causing it not to rev up?