My 64 9.5 sportwin runs great with cowl off but put it on and it starts bogging down, rough idle won't reach top rpm. Remove it while its running picks back up. I assume its an exhaust leak; however I don't see anything that is obvious. It is being tested in a 55 gallon barrel. Perhap it would do better on the lake? Or should it be fine in the barrel? If its an exhaust leak would it likely be the exhaust gasket under the powerhead or the exhaust housing seal? Or both maybe?