motor problems

[the stick]

I have a 50HP Mariner 3 cylinder. The stator went out in June, it was replaced. Carbs checked and cleaned. Now I have a very annoying problem.

The motor runs great when cold, but after running for awhile it starts

acting up. It surges when brining up on plane. Throttle is wide open but boat

runs at half speed, then all of a sudden it kicks in to full speed. We

messed with changing out the coils with limited results. Any ideas??????

[RebelSS]

Yup. Sounds like a fuel delivery prob, aka pinhole in the diaphragm, fuel line, etc. When it does it, try pumping the fuel bulb. If that helps,you have a crack/pinhole somewhere that is causing a loss of fuel delivery pressure. Check you fuel line bulb well, and with it not running try squeezing fuel bulb hard. Any gas leaking at carb diaphragm tells the story. Good luck!

[kfk]

It could be a bad brain box also. In my experience, that's typically how motors act when they go bad.

[jvm1]

I had the same problem somewhat, it was a bad spark plug

[Ufatz]

Loss of fuel pressure in line.

[boatfixer]

If you have a timing light you can alternate it between cylinders while it's acting up to determine if it's ignition related. Simple and easy way to steer you towards spark or fuel. If you have a another can and line, try switching that out as well. If it's a fuel delivery issue, It would have to be a connector sucking a little air or check valve in the bulb sticking shut. Otherwise things like diaphragms filters etc won't "fix" themselves and would be a problem all if the time. You did state that it runs ok cold and will snap out if it. I'd lean towards ignition.