Nissas NS3.5A Cutting out and stopping after 5 -10 minutes of runnind mid to full throttle.

Was given this little outboard from the RV Camp manager where I camp/fish. Great for trolling but problem when revving up to get off the lake quick if wind picks up. I cleaned out carb, replaced fuel line. Engine shows little wear and no abuse. It runs fine at lower speed but when I increase to mid/full range, after about 5-9 minutes the motor starts to stutter intermittently and then soon shuts down completely. Then it won't restart for 10-15 minutes. And during this time if you pull the throttle it doesn't feel normal, like it's binding. I've been told it's symptomatic of the engine overheating, but the water tube spouts out a steady stream of cool water even when the outboard is shutting off. The cylinder head around the plug is warm, but I can continue to touch it without discomfort at the time the motor is shutting off.

Does anyone know what can cause this? I had it into one shop and they said since it was pushing out a good stream of water, and the cylinder head is not overly warm they couldn't figure out why it has the symptoms of overheating.

I don't know if I should pay to get another opinion or just junk the motor. But wish I didn't have to as it seems in such great shape otherwise.

Thanks,

Doug

It may be overheating due to a piston/ring versus block issue. That could be anything from a scored block to lack of oil lubrication.

What Elvin said, plus... as you run faster, there is more heat generated, even in a healthy motor. There is a possibility that the magneto has a part that is failing only when hot. So when it won't start, check for spark. Also check compression. Are you running TCW-3 oil at 50:1? If you don't run enough oil, that sort of problem can happen. The slide-type carbs can be a little stiffer to operate when warm, so it may not be overheating. If your motor is so old that it has points (early 3.5's did), then ignition parts are NLA, so if you have a magneto issue, there's little that can be done to fix it.