1985 Yamaha 9.9 4-stroke won't run unless air intake restricted

[capezig]

Our local youth sailing non-profit had this engine donated and we're trying to get it running right. I changed the crankcase oil, checked the lower unit oil, changed the spark plugs, cleaned a bunch of goo out of the carburetor bowl and main jet, set up a tank with new fuel and have it on a good battery with a hose on muffs for cooling water. It will start easily and run only if the air intake is restricted with a thumb controlling the amount of air flow available. As long as the air intake is restricted and adjusted finely with your thumb the engine runs very nicely. It seems to me that this indicates not enough fuel for the mix, but I can't figure out where the restriction might be. Any ideas would be appreciated.

 

[99yam40]

carbs are not clean enough.
or you have a vacuum leak
Might try a heated ultrasonic cleaning machine

 

[Scott Danforth]

You have a plugged passage in the carb

 

[capezig]

I had the carb off again this evening and tried to soak/air blast/phone wire attack the jet under the plastic plug next to the main jet. It now runs with throttle without having to manually choke off the air intake, but still does not run at lower rpms/idle, without choking off the air intake with a thumb. Does this tell anyone which of the microscopic passages might be the culprit? I really appreciate the responses so far confirming my thoughts...now to find the tiny blockage...

 

[capezig]

This thing is driving me crazy...I have had the carb off and apart 4 times. I have blow air, sprayed carb cleaner and run phone wire through every passage I can find and still the same symptoms. I noticed tonight that the throttle cable casing is broken at the front of the engine...but it does not seem to be stopping the throttle from operating to its full range... How is this goofy auto choke thing supposed to work with the plunger in the little plastic dome? When should it go up and down?

 

[flyingscott]

Is your motor a 2str or 4 str 1985 would more than likely be a 2 stroke. Have you done a compression test.

 

[capezig]

It is a 4 stroke, definitely. It runs fine, as long as the air intake is restricted, I assume to match the amount of fuel making it to the carb. I think I have all the passages and jets clear, but this 'fuel enrichment circuit' with the plunger in the clear bubble on top of the carb has me baffled...

 

[capezig]

Now I have put a carb repair kit to work in it...and still the same issue. Any advice on the correct setting of the 14392 needle valve?

 

[ondarvr]

The needle valve is adjusted to where the motor runs the best, it's not required to be set at any certain numbers of turns.

As for it still not running correctly, dirty carb, vacuum leak, fuel pump, most likely one of the first two.

 

[capezig]

Apparently, I missed on the importance of getting the main and pilot nozzles all the way out to clean out the little tiny holes, especially in the side of the main nozzle. That was done today and the engine now runs perfectly...what a sweet little motor.

 

[99yam40]

thanks for coming back to say what you found wrong with it.
Most do not say what they found.

seems some do not know how to clean everything properly the 1st few tries
hope your post will help others down the road