Tohatsu 5HP [MFS5C] Dies When Put In Gear

[tmitch120]

I purchased a Tohatsu 5HP MFS5C 1.5yrs ago. It has less than 20hrs on it. Last week I pulled out from the slip and got about 50 yards when it died. It started right back up but, as soon as I put it in gear, it died. The engine is used quite regularly and was last used less than two weeks prior. The gas tank and lines are always stowed when not in use.

The next day I put clean gas in it and it started right up. I let it idle for a while, revved it up a bit and after it was warm, put it in gear. It died. Today, I tried some more extensive testing. I let it idle for 5 minutes or more. I revved it up and ran it for a while. I put it in gear. It died. I tried letting it idle once I put it in gear. I tried revving up once I put it in gear. It always dies within 2-5 seconds after it is put in gear.

No matter what RPMs I put it to when not in gear, it never dies, no matter how long I let it run. No matter what RPMs I try to run it at once I put it in gear it always dies. I can not find comparable symptoms in the forums. It seems like it would have to be an electrical/electronic problem but...I really have no clue at this point. Any assistance would be appreciated.

Thanxx.

 

[Sea Rider]

Welcome to Iboats,

If you test that OB say with an engine stand while on muffs and geared forward, will the OB rise revs without dying throughout the throttle range ? Non load and at load while pushing a boat are 2 different conditions.

Happy Boating

 

[pvanv]

Most likely a too-lean condition, requiring a good carb cleaning. But it could be as simple as the shift linkage rubbing on the kill wire, which might have worn through the insulation, stopping ignition. Start by checking spark plug condition. If it's wet, that indicates lack of spark. If dry (or white), that indicates insufficient fuel. Also verify that the oil is not over full.

 

[tmitch120]

Sea Rider, hopefully I can avoid having to take the motor off the boat but, if I have to, I'll try that test first thing. Perhaps they have a motor stand I can use in the maintenance shed on the dock at my marina. That would make the job easier. Thx.

pvanv, I'll check that linkage and kill wire first. There's nothing to drop in the water there. Next will be the spark plug since I think they shipped the engine with a spare plug. I seriously hope it's not the carb with always-clean gas, so-few hours and regular use. If it is the carb I may have to give up on sailboats and stick to motorcycles. Thx.

 

[pvanv]

It's critical to run the carb out at the end of each and every day, unless you KNOW you will be running again in a day or so. Somewhere around 1 or 2 weeks of sitting, the evaporating fuel leaves residue in the tiny passages, and it is quite difficult to remove, aside from a complete disassembly and proper cleaning. BTW, you could also verify that the LU isn't giving too much drag, say from a fishing line wrapped around the prop shaft.

 

[Sea Rider]

Hopefully I can avoid having to take the motor off the boat but, if I have to, I'll try that test first thing. Perhaps they have a motor stand I can use in the maintenance shed on the dock at my marina. That would make the job easier. Thx.

Better take the whole combo out to Terra Firme and perform the test while OB is mounted on transom and subsequently any other test you need to perform on that OB. Much better than doing it at sea, lake.

Happy Boating

 

[tmitch120]

Can it still be a carb or plug issue if it idles perfectly, throttles through to near-full throttle perfectly and once you put it in gear it runs perfectly for just a few seconds before it just dies? It doesn't sputter or anything, it just dies.

 

[pvanv]

Have the fuel pump and filter been checked? Will it restart immedaitely after it stalls? Have the resistance checks been done on the ignition system?

 

[Sea Rider]

Could be anything electrical related, when OB is at load any electrical compponent heats up, shorts, misses, cools down and the story goes on and on. Will need to troubleshoot all electrical components individually. Start checking Ignition Coil..

Happy Boating

 

[TOHATSU GURU]

Take the engine into a dealer and utilize that five year warranty that you paid for when you purchased the engine.

 

[akl2010]

with the motor off (ignition key removed), shift into gear and spin the propeller. I say do this because it sounds like something has locked up in the lower gear unit, or a bearing has failed. If the motor and propeller will not turn over while in gear you have a problem; note that it should not take to much force to turn the propeller while in gear. please let me know results.

 

[pvanv]

with the motor off (ignition key removed), shift into gear and spin the propeller. I say do this because it sounds like something has locked up in the lower gear unit, or a bearing has failed. If the motor and propeller will not turn over while in gear you have a problem; note that it should not take to much force to turn the propeller while in gear. please let me know results.

The motor is non-electric.

 

[akl2010]

The motor is non-electric.

What does that matter? It has a kill switch and ICU.

 

[pvanv]

Firstly, the motor is still in warranty, so it should be a no-charge repair if the problem is not caused by abuse.

Secondly, since no MFS4/5/6 ever had electric start, there wouldn't be any key.

Also, trying to turn the motor against compression by using the prop is borderline crazy. The prop will ratchet in F, and the gear ratio would likely prevent turning the motor in R. No, it doesn't have an ICU... just a magneto ignitor.

Clearly, akl2010 is not familiar with this model.

 

[Sea Rider]

If you want to turn prop to check lower tail cond, while turning flywheel CW by hand, engage gear F or R, will see prop spining slow, near impossible to turn motor by turning prop. Besides stupidity, compression and gear box realted issues.

Happy Boating

 

[tmitch120]

Sorry for the long delay in updating this. My dad finally got the motor off the boat a while back, got it home and checked it out. Ended up that the only thing that was done to fix it was to replace the spark plug. He got it back on the boat and it was fine. I'm still confused as to how a bad spark plug would cause the problems as described but, happy he is back to sailing now.

 

[Sea Rider]

New, old spark plugs can fail at any time, it's a good thing, saves precious boating time to install a new one before attempting to troubleshoot all electrical related parts when you are sure fuel circuit tank to carb works spot on.

You're the third poster that have solved cracy OB behaviours by simply installing a new spark plug...

Happy Boating