I Have 1978 Johnson 35 hp Seahorse, Ive just replaced water impeller and housing as the engine wasnt pumping water. Only to later find that the water tube leading to powerhead was bent and wasnt meeting gromet ontop of housing.
So after a few hours of playing around me and my dad managed to fix it, we then lowered engine into tank (Water Level Just Above Pump) started engine we had a good flow of water from peehole for 8seconds but none from exhaust relief then the water stopping flowing from peehole but the powerhead was still cool and seemed as if water was flowing through engine.
Lower unit then removed hose attached to water tube then flushed water through everything seemed ok.
reattached lower unit ran engine and it pumped water great! then relised i left the window off exhaust housing reattached it then water flow stopped or seems to.
I Thought it was just the water level in tank, so i used muffs with very low water pressure, and it pumps water like a dream
What i will say is it seems that exhaust fumes were coming from peehole after the good water flow stopped, when it was in tank.
Everything else on engine seems good, has had new gaskets cleaned carbs and so on.
Any ideas would be grately apprieciated, me personally i think it might be the water level in tank when running it in their.