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

[Max...]

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.

Pumping bulb when engine idling/dying has no affect - bulb is hard too.

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.

Any ideas please chaps?

[lightning]

How old is the engine? Sounds like a blocked idle jet to me.

My Tohatsu 9.8 (two stroke) is not smooth at under 1400 rpm, never has been, but it never stalls. The idle settles at a rough 1200 and under load an uneven 8-900rpm.

[Max...]

2006 and low hours, very well maintained.

[Chasbroon]

Almost certainly the idle jet. Also once the jet has been taken out and thoroughly cleaned (don't use a wire - use something like a nylon brush hair and wash out in clean petrol or similar solvent) blow out the orifice it screws into. In fact blow out all the holes around the jets. If you haven't access to compressed air use a small diameter plastic pipe over the hole and blow hard.
Good luck

[Max...]

I will check out the carb again then - surprised though as I'm really careful with fuel cleanliness, there's a filter in the pick up and in the carb of course and the carb was cleaned a short time ago. Is the fact it was trolling for a few hours a factor?

As a follow up to my OP I did try a pair of used (but clean spare) plugs and the same issues remained.

[willk]

You've tried it on fresh fuel mix, of course?

[Max...]

Originally Posted by willk

You've tried it on fresh fuel mix, of course?

[willk]

Originally Posted by Max...

Hmmmm

You wouldn't be running on "double" mix - 25:1?

[Max...]

99.99 % sure, I always habitually fill from a 5 litre container to which I add 100ml measured at filling time.

[Locozodiac]

Check gas tank is inmaculate clean along internal mesh filter, carb filter too. Probably your slow carb circuit is bit varnished. Will need to dismantle hole carb, remove all plasitic and rubber parts and soak for at least 3 hours on a proper dip carb clean fluid. Squirt all fuel passages with any good quality spray carb cleaner, assemble back carb and test. Adjust fuel/air mixture screws and slow idle screw back to specs,

Happy Boating

[Max...]

Thanks Loco, what a PITA!

[Max...]

Fookin' outboard engines, one day I'll manage to buy a reliable one...



Stripped it down, carb, all the fuel system - re-assembled and tested but so erratic.

I left it to warm up on 1500 revs or so, then throttled back to 800ish, lumpy but did not stall, revved it up, then when throttle shut it remains at 1500 or so, as you increase throttle it sounds like it's misfiring.

Argggh, fed up with outboards....

What to do next??

[tony t]

Originally Posted by Max...

Fookin' outboard engines, one day I'll manage to buy a reliable one...



Stripped it down, carb, all the fuel system - re-assembled and tested but so erratic.

I left it to warm up on 1500 revs or so, then throttled back to 800ish, lumpy but did not stall, revved it up, then when throttle shut it remains at 1500 or so, as you increase throttle it sounds like it's misfiring.

Argggh, fed up with outboards....

What to do next??

Down the pub

[Max...]

You said it Tony!

Everything that could go t**s-up this week has...

Still, a large Scotch, couple of vinos and a Stella by 8.30 pm and things are looking up already!

[m chappelow]

Wondering if there's a reed valve stuck or sticking at the back of carb if it has some
I had a Yamaha that was giving same symptoms after stripping the carb down twice & cleaning with no improvement i removed cleaned up the reed valves & one was sticking .

[Max...]

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

SamT kindly offered the following too by PM which I'll post up to add to the info:

"Have a look at the coil under the flywheel. AJ was having lots of issues with his, and I had his carb off 2/3 times to clean it, then we thought it was the cdi unit. Turned out the fixed magnets under the flywheel and the coil were rusted. Cleaned these up and the engine ran like a dream..."

[AJ.]

Yep it was a nightmare started to cut out through all the throttle ranges occasionally but would start and then got more frequent over time until it finally died. As SamT said we (he!) tried new fuel, cleaned carbs 3 times, new CDI unit, and then he investigated under the fly wheel. Runs like a dream now half a pull on a cold start and it runs perfectly.

It was very frustrating cause their simple engines definitely needed a pro to look at it.

[Max...]

Just had a look under AJ and it's minty mint, like the rest of the engine it really looks totally brand new under the hood.

As you say this is frustrating as hell - never admitted defeat before but I think I might need to take this to a pro...

[AJ.]

Did you take the fly wheel off cause mine looked minty mint as its a 2010 engine.

[Max...]

[..OP goes back to garage to take flywheel off...]