you sure thats 60s and not earlier ? sounds like your decribing the old fuel pump system on the 18 and 10 evi's you had to pump and then they would suck. 50's.
Those motors can run so fantastically well they are like magic
I HIGHLY SUGGEST you get on outboard motor recyling or whatever and 0rder a impeller kit for it right away.
they get tired and deformed just by staying in the same place