My 1973 65 horse Evinrude was running fine and suddenly developed a
problem. It starts fine, buts quits when it warms up. The spark seemed
fine, so I changed gas hoses and tanks. Then I replaced the fuel pump
and all the fuel lines. Then I suspected the leaf valves, so I took it
apart. The leaf valves look and feel OK. When I turn the crankshaft by
hand I can hear air sighing out of the cylinders on the compression
strokes. That sounds like bad rings, but it has a new powerhead with
about one hundred hours of use. Remember that it starts and runs and
then quits when it warms up!