Tohatsu 9.8 Outboard Stalling

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Jaguar 25

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I have a 2009 Tohatsu 9.8hp, 4 stroke outboard. It ticks over smoothly but when I rapidly open the throttle it usually stalls. If I open the throttle gently it is fine.

I have removed the carburettor and it looked very clean but still gave it blast with carb cleaner and replaced the slow running jet (which didn't seem blocked). All reassembled this morning with fresh petrol and it's still the same.

Any thoughts on what I should look for?
 
Jaguar 25 said:
I have a 2009 Tohatsu 9.8hp, 4 stroke outboard. It ticks over smoothly but when I rapidly open the throttle it usually stalls. If I open the throttle gently it is fine.

I have removed the carburettor and it looked very clean but still gave it blast with carb cleaner and replaced the slow running jet (which didn't seem blocked). All reassembled this morning with fresh petrol and it's still the same.

Any thoughts on what I should look for?
Click to expand...

Did you check that the main jet and nozzle were clean ?
 
Fuel was fresh from the petrol station yesterday. However, when I reverted to a tank of petrol from last October the outboard ran exactly the same.
 
misterg said:
If it otherwise runs fine, but still does this when thoroughly warmed up, then richen up the idle mixture slightly.
Click to expand...

which is the mixture adjustment screw ? (12 and 22 are stop screws)
MFS8A3-9A3-2009-fig-6.png
 
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VicS said:
My "guess" is that there are no adjustments.
Click to expand...

Yes, there isn't a mixture adjustment screw, which I found quite surprising.

Another peculiar issue is that when I manually close the choke, there isn't any effect on the running perhaps suggesting a weak mixture possible caused by a partial blockage in the main jet.
 
Long shot, but it wouldn't be a blocked cooling channel around one of the cylinders would it? If one is hotter than the other....
 
Looking more closely at the stripped down carb and the Tohatsu parts diagram, the main jet (item 1.3) is clear. I cannot fully tell if the main nozzle (item 1.7) is clear but the central longitudinal bore is clear. Can't see how to remove it as it appears to be firmly fixed in place. Also, the main jet is "in series" with the slow jet (item 1.6) which I do not understand. The route for fuel must be through some bore interconnecting the bore housing the main and slow jet and the bore housing the main nozzle.

It could be that the way it runs is very lean and the tendency to stall is something I need to live with although it didn't seem bad yesterday.s

Any thoughts?
 
Sounds like the engines not getting enough petrol....check the inline filter to see if there's any water trapped inside preventing full flow.

Its constantly happening on my 2.5 yamaha. Cuts out when you try to accelerate quickly.
 
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I have a Hyundai 9,8 hp. It should be the same as Tohatsu. I had this problem. I think it was two reasons. Low speed jet in carburetor. And:
The motor has spark plugs which have a small diameter. This means small insulation distances. The CD ignition unit does not know , which spark should be ignited, so it gives the spark for both each time.
There is one coil unit. If the spark plugs are not "in balance", so that one of them sparks easier, so the energy will be discharged in that plug. If that plug is not in turn to ignite, the engine stops when one spark fails.
Buy new plugs and forget the manufacturer specifications and advice from your "professional" friends. Adjust the gaps in the plugs to about 0.6 mm, that is remarkably smaller gap as specified. Clean also the carb jets carefully.
These actions may help.
 
Ignition came to my mind as well. In the days of my youth when cars had just one HT coil, these symptoms were a sign of the coil breaking down and unable to take sudden high demand when the pedal was floored.
 
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