Nissan 18 2-stroke (NS18E2) quits once warm...?

Hi All,

I have a 1999 two-stroke, 18 hp Nissan motor. Its in good shape, has been running well this summer, and has fresh fuel and a strong battery. Cleaned the fuel filters a couple of weeks ago (and they weren't dirty). Took the boat out yesterday and the motor started and idled well. Pulled away from the dock and it felt strong. Ran about 3-4 minutes at medium RPM and it started to stumble and then quit. Checked everything over, gave it a rest, and it restarted and went through the same sequence again. Tried it again today in the yard with a garden hose supplying cooling water. Started well and idled well. I let it run in neutral at low RPMs and it quit after about 5-10 minutes. Before it quit the RPM dropped and it stumbled for 20-30 seconds sort of like it's running out of fuel...

Suggestions for what I should check first?

Thanks!
-Bill

Could be a number of things, including electrical, but likely a fuel starvation issue. I would check over the entire fuel system, from the carb all the way back to the strainer in the tank. Understand that the fuel line is under vacuum, so a slight air leak could cause that.

Thanks Paul! The Tohatsu folks suggested that I look at the water pump impeller first. Sure enough, it's falling apart. I know I saw cooling water was coming out the top port when I was running it and I don't think it got very hot. Can a lack of cooling water cause an engine shutdown? Or perhaps a high engine temp causes poor running? I also found that the thermostat is stuck in the open position for what that's worth.

The good news is that compression with a cold engine is still fine. We'll see how she runs with a new impeller.

Best,
-Bill

A stuck stat will cause issues, because the motor does not get hot enough. Then add a shot wp, and you get weirdness. But it still sounds like a fuel starvation issue.