Outboard plug fouling

[CliveG]

Hi

I am having a problem with my Tohatsu 3.5 - 2 stroke outboard.
I normally us the outboard the go out to our swinging mooring, about 5 minutes run each way.

The spark plug is getting fouled with a wet brown deposit and has had to be cleaned prior to starting each time.
This has been getting worse for a while.
I did a longer run the other weekend and now the engine refuses to start at all.
I suspected the head gasket first and removed the head.
I can't see a problem with the gasket.
I have now removed the power head and split the crank case.
A lot of brown deposit and the crank has rust spots on it.
I suspect water getting into the crank case but can't find any obvious route past the gaskets.

Has anyone had a similar problem?
What is the cause?
Do I just put it all back together with new gaskets having cleaned up?

 

[jac]

Have the 2.5 hp tohatsu 2 stroke. I noticed that the plug fouled with brown liquid. Turned out to be the oil from the fuel (I think) the residue I think had dissolved back into the fuel so was getting worse over time.

Proper clean of the carb - strip down, lots of cleaner, started first time no liquid. Not sure how the rust got onto your crank but if you've eliminated that, start with the basics. Is fuel getting through, getting a good spark?

 

[macd]

A lot of brown deposit and the crank has rust spots on it.
I suspect water getting into the crank case but can't find any obvious route past the gaskets.

Has it been dunked in the oggin?

 

[VicS]

Using correct plug NGK BPR6HS-10 or BP6HS-10 (gapped at 1.0mm) ?

Always worth trying a new plug in case of difficulty

Using the correct fuel/oil mix and the correct type of oil?

Not using stale fuel ?

Carb not flooding ?

Not tampered with the carb mixture setting? You could try weakening it to see if it helps.

Do you shut the fuel off and allow the engine to run the carb dry after use? It might help to do so if you dont already.

About the only way you are likely get water into the crankcase is via the inlet ie the carb. unless the seals have gone but then it would have been difficult to start

 

[CliveG]

The outboard has not been dunked.
I have abut 5 plugs for it and the new ones work for a while and get fouled.
With a clean plug it normally starts quite easily.
The fuel oil mix could be a bit heavy on oil.
I will thin that down a bit - it is new this year.
The oil is 2 stroke mix from a local garage.
I normally run the carb dry as I don't want the fuel smell in the car on the way home.

Got the motor striped down so I will clean it all up and when the new gaskets arrive put it back together and see what happens.

Thanks for the help.

 

[VicS]

The outboard has not been dunked.
I have abut 5 plugs for it and the new ones work for a while and get fouled.
With a clean plug it normally starts quite easily.
The fuel oil mix could be a bit heavy on oil.
I will thin that down a bit - it is new this year.
The oil is 2 stroke mix from a local garage.
I normally run the carb dry as I don't want the fuel smell in the car on the way home.

Got the motor striped down so I will clean it all up and when the new gaskets arrive put it back together and see what happens.

Thanks for the help.

I think I would pay a bit more attention to the oil. Mix ratio and type

TCW3 outboard two stroke oil is recommended although I not expect any trouble with a little outboard from using any two stroke oil.

 

[Beyondhelp]

If you only idle around at light throttle you can lean the mixture out quite a lot. Does it burn smoky? Try 75:1 instead of 50:1, but ONLY if running at light loads. FYI modern (ish) 2 stroke engines with controllable mixture systems run as high as 100:1 under light loads...

 

[macd]

The most common causes of plug fouling on stinkwheels:
premix too oily or wrong type of oil;
too cold a spark plug (the higher the number in the NGK examples Vic mentioned, the colder the plug);
wrong plug gap;
too much running on light loads (so give it some welly);
spark too weak.

 

[jac]

The outboard has not been dunked.
I have abut 5 plugs for it and the new ones work for a while and get fouled.
With a clean plug it normally starts quite easily.
The fuel oil mix could be a bit heavy on oil.
I will thin that down a bit - it is new this year.
The oil is 2 stroke mix from a local garage.
I normally run the carb dry as I don't want the fuel smell in the car on the way home.

Got the motor striped down so I will clean it all up and when the new gaskets arrive put it back together and see what happens.


Thanks for the help.

After mine was laid up I used the recommended 25:1 and put a tank load in at that mix when i brought it back to life. I was shocked at how quickly the plug fouled - burnt 1 tank of fuel and brand new (correct) spark plug was shot even though I quickly got it up to 3/4 throttle. Diluted the fuel to get back to 50:1 and fouled the second, probably due to there still being a lot more oil floating round than I thought.

Thorough clean and so far it's back to "normal"

 

[Stemar]

Is the float chamber valve leaking? Too high a fuel level would cause rich running, which could account for the symptoms. The "needle", from memory is a plastic cone that does wear over the years. Also, rust in the crank case suggests a bit of moisture's got in there. If it went in with the fuel, a bit of corrosion on the valve seat isn't hard to imagine.

A sticky float "hinge" would do it as well.

 

[lw395]

I would suspect the fuel:air mix is rich.
Could be float height
jet worn by cleaning with metal tools
dirty or worn or sticking float needle valve

I would take the float bowl off and check the float actually stops the flow of fuel when raised to the correct height.
Also nothing jamming the float?

Also check the silly things like the choke mechanism actually disengages.