Model # 357P9A Serial # 1012 U S Marine Power Hartford, WI. 2 Cylinder Crossflow Induction There seems to be an exhaust leak inside the cover. When I take the cover off it runs fine, when I put it on, it starts choking to death at idle. The vent in the cover is free and open. When I take the cover off I notice a small amount of exhaust smoke whirlign around but can't see where it is coming from. Head gasket peerhaps??