Boat motor won't turn over unless...?

repair or replace starter motor.

replacement is an outrageously expensive proposition.

two different starter motors were used on that engine...the prestolite motor is out of production -- I found a brush set at my local OMC parts house a couple years ago, but it was about $50.

I bet a local starter motor repair shop can find a set to match, a lot cheaper.

If you have the American Bosch starter, shouldn't have a problem.

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BTW, your motor does not have valves, as it is a 2-stroke engine.

If it won't turn over unless the plugs are out, it sounds like the valves that supply air and fuel are stuck shut, if you're lucky. It could be much more serious, like pistons, rods or other critical engine parts. Lots of bad things happen to motors that sit a long time without being used. If you're a good mechanic, disassemble the engine completely, soak parts in carb cleaner, reassemble and give it a try. Otherwise, check the value of the engine and decide if you want to spend the money to have it repaired. That operation can be quite expensive. Good luck with it.

It sounds like your starter is weak. When they start going bad they draw more amps and it won't turn over the engine as fast..or fast enough to get it to start....so when you remove the plugs....it's easier on the starter and lets the engine turn over. I would rebuild the start...even if it doesn't need it right now...it will be one less thing to do later down the road....but I'll bet that will fix your problem.

sounds like compression is building up and not being able to escape is the reason for it only turning over with the plugs out.Take a closer look at the exhaust outlet valves ,they may have become seized or are being stopped from opening.Check manifold and exhaust are not blocked also.

take the plugs out DISCONNECT THE BATTERY

squirt fogging oil in to each cylinder and turn it by hand using the flywheel you should beable to turn it

turn it about 4 times get everything soaked with the oil put the plugs back in and see what happens dont forget to reconnect the battery good luck