Some advice please, 1989 9.9 yamaha

[Daviet]

Let me start out by saying that I have not worked on many 4 srokes and not much of a history with Yamaha.

A little history on this engine
1989 4 stroke 9.9
Owner has had trouble with the engine starting and stalling for quite a while and had taken it to several repair shops and one dealer. No one was able to help him out with his problem and I said I would try to find out his problem.
You could pump the primer bulb until firm and the engine would start and run until the carb ran dry. I was thinking fuel pump but it would not stay running by pumping the primer bulb. Took the carb off and tried blowing into the fuel inlet and it would not pass air.
Replaced the needle valve and the engine will start and idle great on the hose.
Put the boat in the water to test it under load, will start and idle in gear great. When you try and apply power the engine will stall, it will restart without any problem and idle great.
If you restrict the air flow by holding your hand over about 1/2 of the air intake the engine will acceralate properly and run at high speed without any problems.
I am not sure of the float setting as the carb has been apart several times by other people. Could any one give me the correct float settings?
Anyone have any ideas that might help me out?
Sorry for the long post, just trying to give you the whole story.

 

[sdsaw]

Re: Some advice please, 1989 9.9 yamaha

Repair shops couldn't figure it out?
From what you are describing, it sound like a dirty carb
All the choke parts hooked up correctly?

Float height is (with carb upside down), measuring from bottom edge of the float to the mtg. surface of the float bowl
25.5 +/- 0.5mm or 1" +/- .020

While you have the carb off, I would unscrew the main jet and pull the main nozzle. Make sure that all the little holes are clean and make note that the cut out faces the intake manifold

Pilot jet, accessible by pulling plastic plug (with o-ring) next to the main jet

There's another pipe (starter pipe) that is above the drain screw that should be checked and cleaned

Pilot screw removed and tip checked for damage

Check for blockage of the 3 small holes in the top of carb bore
Another small hole just inside of the main nozzle
Check for blockages and clean all these areas.

Hope this helps and get back with the results

Scott

 

[jeffersondodson561]

Re: Some advice please, 1989 9.9 yamaha

If this is the one with the plastic diaphram housing and the hoses routed on top of the carb, if it is these can be tricky carburetors. I found that that year seloc manual had the best paper illustrations for this carb. One problem that threw me was that box toward the rear of the engine acts as the PCV valve and a restriction can cause problems. Open up that box carefully and try not to tear the gasket and look for air restrictions. Fourstroke carbs are a lot more unforgiving than two stroke carbs and now virtually every manufacture recommends ultrasonic cleaner for proper cleaning. A lot more smaller orfices.

 

[Daviet]

Re: Some advice please, 1989 9.9 yamaha

Thanks for all the information, I will try the suggestions mentioned and get back and post the results. It will take a couple of days but I will let you all know.

 

[rodbolt]

Re: Some advice please, 1989 9.9 yamaha

nothing on that engine remotly acts or is a PCV valve.
some had an evap canister to absorb gas vapors at engine shutdown and intake vacum would draw the vapors out of the charcoal cannister at restart.
however by your statement,
I can cover the intake and it runs.

the float is ok, the fuel pump is ok the cold start enrichment circuit is ok.
the main jetting circuit is NOT ok.
by covering the intake your simply forcing the carb rich bypassing the main jetting circuits.
time to clean the carb.