Surging idle on 9.9 high thrust.

Apparently there’s a fuel bowl drain under the carb that you can use to drain out any gum or residue that may be affecting carb performance. Had a similar issues on my old 8 hp Yam HT.
 
AndrewH said:
Pretty easy to explain through the video... where do I start?

replaced main fuel/water separator but no difference.

Click to expand...
AndrewH said:
Pretty easy to explain through the video... where do I start?

replaced main fuel/water separator but no difference.

youtube.com

Yami 9.9 High trust

youtube.com youtube.com
Click to expand...
my two cents

try the easy stuff first.

there should be a small fuel filter under the cowl of the motor (Fwd bottom) change or inspect that. could also pull your spark plugs and check the condition and spark( probably not the issue but worth a look) next i would look at the carb make sure the choke linkage and throttle linkage is all connected properly and both function as they should and if it has an electric choke option that it isnt shorting and being opened and closed through a short/corroded connection.

last Try to Clean out the carb. you can try cleaning in situ but its usually better to remove and dissasemble.

clean out with an aerosol carb cleaner or soak/bathe the whole carb in carb cleaner or a product like sea foam a few hours is ideal. blow out the jet(s) with dry shop air, it could be dirty or gummed up.

i have had carb issues on my 2008 yamaha high thrust kicker turned out to be a dirty carb.

good luck
 
AndrewH said:
Pretty easy to explain through the video... where do I start?

replaced main fuel/water separator but no difference.

youtube.com

Yami 9.9 High trust

youtube.com youtube.com
Click to expand...
Def try the carb clean, prob one of the tiny orifices is plugging with silt or crap in the fuel. I’ve also heard that running them dry every time they are used is the best way to keep from having common carb issues.
 
Check oil level as well as there is a sensor that slows motor down if oil is low....
 
Do you have a compression tester? If so, pull compression once you're sure fuel delivery is solid. Then you'll confirm the motor is healthy. Racing up and down seems like a vacuum leak too, any chance you knocked something off?
 
Sounds like it could be an air leak. But I’d probably be pulling off the carb and cleaning the jets first and checking gaskets.
 
Could be junk floating around in carb but also sounds like 1 cylinder is cutting out so only running on one then it catches and back on two. Check plugs, plug caps/wires and coils. When it starts to cut out be ready with some insulated plyers and pull a plug wire off one plug..if nothing happens that cylinder isn't firing..if it quits the other one isn't firing. Just watched it a 2nd time...take the carb apart clean with carb cleaner and blow it well out with compressed air.
 
Last edited:
I had crap in my carb, and did just what you are saying. Pull it out and clean it. Easy job to do, and easy to learn yourself.
 
Does that one have an IAC on the carburator?


Take a picture of the carburetor so we know exactly which one it is
 
Drain float bowl on carb first, give a couple shots with primer bulb when the drain is open. Sea foam treat the fuel, then sea foam or some sort of intake/carb/combustion chamber cleaner. If it still does it check the electronic choke unit. It has nothing to do with spark or any of that trust me. I’ve had 4 of them motors it’s always too much fuel, lack of fuel supply or choke. 90% it’s a fuel/carb quirk.
 
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