Tohatsu 6HP stalling after 30 minute run

[unitfive]

I need help to troubleshoot an issue with my 2009 Tohatsu 6HP (MFS6B). The motor starts with only a couple of pull and will run smoothly for 30 minutes usage before stalling. It will start again after 10-15 minutes wait but will only run another ~10 minutes before it will stalls again. It will run only at ~50% power after a stall. I found a good stream of water from pee-hole and the water was COOL to the touch. Gas is new 89 octane and vent is open. I still run the motor in breakin mode since it has ~12 hour total run because it has been in storage until this season (8 hour breakin run during first month then few hours this year with the stalling issue).

• I already changed low gear and motor oil
• I already changed the spark plug and making sure the gap is correct. The previous spark plug looks clean.
• I already tired cleaning the carburetor and jet by taking it out and soaking it in car carburetor cleaner
• I used new 89 octane oil and gas container vent was open
• Motor oil warning light was not on during run.
• Everything still in new condition under the cover including the wiring.
• I checked for water from pee-hole often and always found a good stream of COOL water (but the engine block feels hot to touch after a stall).

Any suggestion on how to diagnose issue?

 

[rsnyder518]

I have a Tohatsu 6HP also, and I'll warn you up front that I'm not a mechanic! But I had an issue similar to yours a few years back. Turns out that a component in the ignition system (the igniter if I remember correctly) was conking out when it got hot.

I'd check for a strong spark when it's cold (so you have a baseline) and then run it until it conks out. Then check the spark again and see if it is there at all or if it's noticeably weaker than the baseline. If the spark is not present or is weak after the engine is hot, then the culprit is somewhere in the ignition system. Actual mechanics may have more thorough diagnostic procedures from that point! The factory service manual has lots of trouble shooting guides as well. Good luck.

 

[Sea Rider]

Depending on the model you have : exiter coil, cd, ignition coil, pulser coil, igniter. Heat related issues are the most PITA to diagnose. Works ok when cold, misses when hot and the cycle goes on eternally.

Happy Boating

 

[unitfive]

Thanks rsnyder518 and Sea Rider.

My 6HP only has igniter. It seems odd for it to fail just sitting in storage for a few years. The igniter and all the wires still look new.

I will check for spark once I find a chance to take it out for another spin.

 

[MattFL]

Also make sure the gas tank vent is open.

 

[Sea Rider]

It it's a single electric component (Igniter) that's the culprit. Don't know that model, only work with 2 stroke versions, strange that at least doesn't have one more electrical element located around flywheel that powers the Igniter. ? A closed tank's air vent shuts engine down very fast specially if running at wot and will not restart engine back. When that happens could have a sucked looking fuel tank.

Some times moisture gets in and makes electric components to fail, check that all electrical grounds and its contact points are immaculate clean and in shinny state. Somebody here said something about heating CD's with heat guns, ovens at a very low temp for some time as to dry moisture out. Do same and see what happens ?

Happy Boating