Motor runs great but will not idle with the cowling on. At idle when I take the cowling off it’s full of exhaust fumes. I pulled the power head and replaced the exhaust gasket but still have the same issue. I can idle all day long with the cowling off and compression is fine. As soon as you throttle up the exhaust starts to come out of the prop and the fumes clear up. Does the 120 hp have any type of idle exhaust bypass?