Had a similar problem on an old evinrude, turned out to be the coils.
Problem got worse over time until it was almost impossible to start. The
coils dry out from age. My marina operator knew what it was as soon as he
saw how old the motor was. Had them replaced and it ran great for years
afterward. It was only a 10 horse though.
"Robert Olson" wrote in message
...
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!