The problem with the 15 hp is as follows.

I bought this motor two years ago from a guy who claimed to be selling it
for the wife of a deceased friend. He didn't have much info on the engine
except to say it had not been run in at least 5 years. (I willing to bet
it
was like 10 or more years.)

Although originally I could not get it started, I've now had it serviced
by
three different repair shops, all with OMC backgrounds. It's been
decarbonized, had the carburetor cleaned and rebuilt, new plugs and had
numerous other minor issues resolved. The water pump hasn't been
overhauled,
but the mechanics have all claimed that the impeller is fine as the engine
produces a sufficient "pee-stream." However, the big problem hasn't been
solved.


If its been sitting for that long I would replace the impeller ASAP.

When the engine hasn't been used overnight or for a few days, it starts on
the first or second pull and will idle OK. It will also run fine under
full
power on that first run and push our 14ft aluminum skiff at 20-25 miles an
hour. From that point the reliability goes downstream fast and has me
ready
to use it as an anchor.

The fun starts when the engine will not idle after being run at full or
half
throttle. It will also not restart easily if it is hot and/or has stalled
out. You can sometimes get it started if you override the neutral-start
interlock and immediately give more throttle than the "over-rev" limiter
in
neutral will allow. I know it's dangerous and for that reason won't let my
kids drive it. Letting it sit for a while, an hour or so, gives you a
better
shot of restarting it, but not reliably and/or keeping it running.

Ironically, when I've picked it up, all the shops have told me how great
it
runs in the test tank; they claim it starts right up, idles nicely and
runs
as well as can be expected for this age motor. I don't doubt that it does
(in their test tanks), but I think they're all missing something. On the
other hand, I'm sure they think I'm neurotic about this engine.

Any thoughts suggestions or insights would be greatly appreciated.

Bill Lav

Have you checked the fuel system for adequate venting?
If not vented properly a vacuum can develop in the tank causing the problem
you describe.
Next time it happens try removing the gas cap and check for a vacuum.