Tohatsu 9.8 won't idle, rough, cutting out...

[AJ.]

Mine had a bit of corrosion and dirt on the coil and the coil may have been making contact with the magnets so check that and while its off spray some corrosion guard in there for good measure

[Max...]

OK, starter off but not sure how to lock engine and remove flywheel.

Having said that though I can clearly see from underneath and rotate to see all the magnets and coil - they really are brand new and you could eat dinner off the inner engine - all the parts are mint throughout...

[landlord]

Is this the first time you've used this engine at prolonged low speeds ?

I had exactly the same issue many years ago with an 18hp Evinrude. Cruise / WOT it ran great. Slow river use and it would continually cut out !

Continually had to remove plugs and clean them. It was purely down to oil / petrol ratio with the plugs fouling after prolonged slow running.

Next time it happens it would be worth removing plugs immediately to see how bad, if any, the fouling is.

[AJ.]

Hmmm I would take it to a mechanic gets to the point where you have done all you can and wasted hours on it. Find someone decent and I'm sure they will sort it in a couple of hours and you get to enjoy the end of the season

[m chappelow]

Originally Posted by Max...

Thanks Mart, TBH not sure what a reed valve is or looks like?? Can you help a bit more?

."

It's usually just at the back of where the carb bolts to the engine block ,
It's basically a one way valve for the fuel/air mix to go through after its been through the carb ,

Just a hole that's got a number of really thin spring metal flaps that open & close
It's supposed to stop fuel / air mix blowing back back into the carb
Sometimes one or 2 can stick shut , get gummed up or even get bent in the open position or even break off ,

usually quite easy to take apart & clean as long as your not rough with them .

[Max...]

Originally Posted by landlord

Is this the first time you've used this engine at prolonged low speeds ?

I had exactly the same issue many years ago with an 18hp Evinrude. Cruise / WOT it ran great. Slow river use and it would continually cut out !

Continually had to remove plugs and clean them. It was purely down to oil / petrol ratio with the plugs fouling after prolonged slow running.

Next time it happens it would be worth removing plugs immediately to see how bad, if any, the fouling is.

No, done trolling before and plugs got slightly oiled but I changed them anyway - we had a blast after and it was fine at WOT etc - just low speed erratic idling.

Mart - pretty sure I don't have a valve like that on here.

[slate1234]

try sraying seafoam through it or mercury power tune, just do what it say's on the can it may just be a bit of carbon build up

[Locozodiac]

If engine is working ok at medium to full wot rpm. If it's just a slow speed erratic idle issue, assuming carb's slow circuit passage is in inmaculate clean condiion, just need to adjust fuel/air and idle screw properly to factory specs.

Happy Boating

[Max...]

Tried it again today Loco, it's misfiring like mad and not at all happy at any speed now. I'm really going to have to call in a pro on this one.

[Sunstreaker]

I feel your pain man

[Max...]

I left this in the garage unit I had time to look at it again. Stripped the carb (again) 2 weeks ago and it's been sitting in solvent for 10 days, reassembled today and the fooker is just as before, double bolloc£s.

Really beyond me, been through everything, just need to get it fixed somehow so I can move it on. The legendary Tohatsu 9.8 has never lived up to its reputation for me...

[spartacus]

Have you adjusted the carb idle screw? Try one full turn from fully seated for starters and see if it improves. What about the fuel pump? Diaphragm kits for Tohatsu are excellent quality.

Once you rule out fuel, I'd take a closer look at the HT leads.

[Max...]

Thanks Spartacus, I will look at that. The fuel pump diaphragm looked fine but will look again, do you have a link for the kits?

[Peter Bryson]

Max

We a have seen a large number issues with engines like yours in the last two years -far more than we used to see in the past.

Your problem is almost certainly "gunging up" and contamination of the fuel caused by the ethanol "bio-fuel additive" in your fuel.
This additive is now added to all the petrol sold in the UK and EU (the USA doesn't have that problem). Basically if the old petrol fuel goes stale in the carbs, the biofuel additive will form a very thin film on all the jets, inside carb surfaces etc etc

Stale fuel now happens a lot quicker than it used to. The additive makes no difference in cars, because most cars are used regularly- however marine engines often sit idle for months at a time. We have seen cases of engines left with stale fuel going off in just 6-8 weeks, (not 6-8 months that it used to take for fuel to go off)

Whilst you have obviously cleaned most of the insides of your engine, my suspicion would be "bio-gunge" remains either inside the carbs or especially stuck to the jets and inside the jet passages. Quite possibly there are also issues in the rest of the fuel system.

In and around the jets, the bio-fuel is very sticky and you will find it is a lot more difficult to clean off than the "old" petrol used to be.

If you get really stuck, please give our workshop manager Andy a call on 01756 792335. He is pretty good at diagnosing these issues.

Peter Bryson - Pennine Marine

[kerny]

My Tohatsu 3.5 did the same and my mechanic said exactly the same as you

[willk]

Peter Bryson, would you recommend running an engine like this with the fuel supply removed - until it cuts out - as a prevention measure? I always do this with mine and so far so good.

[kerny]

Originally Posted by willk

Peter Bryson, would you recommend running an engine like this with the fuel supply removed - until it cuts out - as a prevention measure? I always do this with mine and so far so good.

That's what I was advised to do willk and also pull the choke out to empty the carb.

[Peter Bryson]

Originally Posted by willk

Peter Bryson, would you recommend running an engine like this with the fuel supply removed - until it cuts out - as a prevention measure? I always do this with mine and so far so good.

Yes - definitely a good idea to disconnect the fuel and let it run out on idle. Also a very good idea to take all your old fuel from the tank(s) and use it in the car or lawnmower in order to start fresh with new fuel at the start of the season.

This biofuel gunk is a nightmare to get rid of using the traditional techniques of cleaners airline etc

regards Peter Bryson

[Max...]

Peter, sorry for the delay in replying but wanted to check my memory after seeing your post and believe it or not the engine has always had a 'Penine Marine, Skipton, N. Yorks' service/sales sticker on the top of the hood!

I am pretty carful about fuel and it was new fuel in the engine for sure for the Devon holiday when the issue started, just to repost from my OP:

---------------------------------

"Been on the River Dart this last week - engine has been running fine all summer until this week. After the first day's pootling on the river at 5 kts or so it started cutting out at idle/taken out of gear towards the end of the day. Got slightly worse for the next two days and was a real PITA when trying to manouver in the harbour as each time into neutral or if trying to go dead slow it died. Out to sea at other rev ranges or WOT it was fine and got full power.
Cleaned carb about 15 hours ago and it was spotless anyway, new plugs then too.
I checked plugs after issues above and they did not look too oily but cleaned them to no affect.
Just had it in water bucket and the same again, will not happily idle below about 1400, drop it to less and then 1200 and it gradually gets rougher and rougher, more erratic, slows and dies."

-------------------------------

The trolling definitely seems to be to blame.

Sadly you are a million miles from me now - any more advice you can offer with your experience?

[Max...]

Hi Peter, that is very kind of you, I will do that.