Fairly new 9.9 HP will not start or run at idle speed

[slowpoke1033]

Happy new year everyone,
I have just joined and am impressed with experience and expertise on this forum. Hope someone can give a hint on how to approach solving my problem.

After a couple of years satisfactory service, my 2009 Merc 9.9 has begun to simply refuse to start or run at idle. I have to set the throttle at least halfway to full speed to get it started, and cannot go below half speed or it dies. In order to use it I have to start at high rpm, then quickly turn the throttle down to engage the gear and twist it right back up before it dies; obviously not a good way to treat this motor. I just installed new spark plugs to no effect, although the old ones didn't look that bad - a little blackened. I have maintained it per the manual. Under the hood, it still looks pristine and there's no obvious problem visible. I think there is probably some adjustment out of spec, but I don't know where to start.

Any assistance would be greatly appreciated.

 

[MH Hawker]

Re: Fairly new 9.9 HP will not start or run at idle speed

sounds like a float problem in the carb from the description, but I am not all that up on 4 strokes.

 

[Star]

Re: Fairly new 9.9 HP will not start or run at idle speed

I have owned an 05 4 stroke 15 (Same engine) for 5 years mine did the same thing last spring. Very small passages on this carb idle circuit. The carb must be removed, and soaked in a srong carb cleaner. Running seafoam through it may work but a good soak is better. Be sure all rubber and plastic parts are removed before you soak it. A shop around here will get $150 plus 65 for carb gasket kit.

 

[slowpoke1033]

Re: Fairly new 9.9 HP will not start or run at idle speed

I have owned an 05 4 stroke 15 (Same engine) for 5 years mine did the same thing last spring. Very small passages on this carb idle circuit. The carb must be removed, and soaked in a srong carb cleaner. Running seafoam through it may work but a good soak is better. Be sure all rubber and plastic parts are removed before you soak it. A shop around here will get $150 plus 65 for carb gasket kit.

Thank you Star, that gives me a great place to start.

 

[oldman570]

Re: Fairly new 9.9 HP will not start or run at idle speed

A can ofg Power Tune bought at a Merc dealer will clean any varish in the carb and is fasrer than Sea Foam. Use as dericted on the can and see if it dose the job. If not, then a carb removal and cleaning/rebuild should be done. Sea Foam works when mixed with the fuel and is more of a preventive than a quick acting cleaner. By turning the idle jet in till lightly seated, and counting the turns as doing, and spraying into the idle jet will clean the idle circut of the carb. Replace the idle jet into the carb till seated and backing it out the number ot turns counted when removed will get you very close to what is needed to start the motor. Run the motor, in a barrel till warmed up, and set the idle jet with the motor in FWD gear will finish the job. Running it on muffs will not get the correct setting as there is no backpressure on the exhaust that is needed.JMO
Oldman570

 

[quicktach]

Re: Fairly new 9.9 HP will not start or run at idle speed

Check that fuel filter is clean. Blackened plugs could mean to rich a mixture [burning oil]. Sounds like a good carb cleaning is needed, followed by set up. I'd also try the 'mechanic in a can' [decarbonizer] too [availble at your Merc dealer]. Don't go adjusting anything yet, till it's cleaned up!

 

[slowpoke1033]

Re: Fairly new 9.9 HP will not start or run at idle speed

I have disassembled and cleaned the carb, replaced the fuel filter, replaced spark plugs, and bought fresh gas. I changed the crankcase and gear oils while I was at it. I started it and it idled ok for a few moments, making me think all was well. However, it quickly died and will not start or run at idle. It will start and run at greater than half throttle, but as soon as I ease off the throttle even slightly it dies.

The only thing I haven't changed is the fuel pump. Does anyone think these symptoms might be due to a malfunctioning fuel pump? I disassembled it and didn't see any obvious cracks in the diaghram, but it's really thin and small. Thanks for any tips.

 

[Star]

Re: Fairly new 9.9 HP will not start or run at idle speed

Hey slowpoke, the idle circuit that clogs is a very small hole that runs across the top of the ventury and shows up as a small hole behind the throtle butterfly. This supplies fuel when the butterfly is closed the fuel is metered by the idle adjustment screw under the brass plug on the outside of the carb. this is your problem for sure. What kind of carb cleaner did you use and did you submerg the whole carb.

 

[MH Hawker]

Re: Fairly new 9.9 HP will not start or run at idle speed

Did you use compressed air to blow it out , Personal I use a piece of fishing line to go through the small ports just to make sure their cleaned, and I would replace the float needle just because that is very often the cause of dieing at idle. It wears and sticks.

 

[quicktach]

Re: Fairly new 9.9 HP will not start or run at idle speed

If your tiller is greater than half throttle and you ease off the throttle slightly, resulting in it dying, that suggests that perhaps your butterfly is closing too soon and you're starving the engine. Check all your linkage adjustment....watch the butterfly as you operate the tiller handle from over half throttle and back down. If that seems ok, do the same thing but watch the advance linkage to see if the trigger coil plate is being pulled back to soon, cutting the engine. I'd check your timing too.

 

[ENSIGN]

Re: Fairly new 9.9 HP will not start or run at idle speed

The idle jet or passage is still clogged.The best way I have found to clean these is to use a ultrasonic cleaner.The passages in these carbs are very small and clogg up very easy even with what looks like clean gas.

 

[slowpoke1033]

Re: Fairly new 9.9 HP will not start or run at idle speed

I took my carb apart again, and cleaned all the parts more thoroughly as was suggested. I soaked every little piece and threaded a wire fishing leader through all the jets and holes. The pilot jet seemed to be clogged, which was probably my problem. The motor now starts and runs fine, so thanks for everyone's help. This forum really helped me out.

 

[oldman570]

Re: Fairly new 9.9 HP will not start or run at idle speed

Glad to hear that your troubles are now gone. Some will not leave us on here know how everything worked out. Come back anytime.
Oldman570