Tohatsu 9.8 4-stroke dies after 20 min of warming up

[SailerJon]

I just bought this used motor and sailboat last season. I'd guess the motor is 4 years old? Used it once last year. Admittedly, I used ethanol gas. It didn't run well. Ran a little and died. At the end of the season, I drained the gas in the engine via running the engine. And started this season (2022) with a new spark plug, change of oil and the right gas. Now the engine will run for about 20-25 minutes, then die. And is difficult to start unless I wait for many minutes. Today, I tried putting SeaFoam in the gas. No help. Any ideas? Thanks!

 

[MattFL]

Does it start easily after cooling off, temperature wise? Or do you have to wait some period of time regardless of how cool it gets? I would first check the vent on the fuel tank, make sure it's open. Next time it quits, open the gas cap and listen for air sucking in. Then see if it will easily restart. If that is fruitless then second I would run it until it quits, then immediately check to see if it's getting spark. Remove a spark plug, put it in the spark plug boot, touch the outside of the spark plug to the motor and pull the rope. You should see a bright spark. There are also spark testers you can plug in-line with the spark plug wire if you feel uneasy about the first method.

 

[pvanv]

OK, always a good idea to mention actual model. MFS9.8B? Always prudent to run the carb dry at the end of the day. Grab a cheap IR thermometer to see if you are overheating. Is it peeing well, and is the stream either cool or slightly warm?

 

[SailerJon]

Thanks for your responses. Update. After a very long effort to start the engine, it started. Not sure why. I ran it about 2 hours. Stream looked good. Didn't feel hot on the top. When I reduced the rpms for docking, and put into reverse, it died. And I couldn't restart it for 10 min. Then when it started briefly, it was rough and wouldn't keep running.

 

[pvanv]

Might well be time to clean the carb. Properly.