9.9 - 4 stroke idle problems

[sullivans790]

I have a 9.9 EXHY. I use the motor for walleye fishing *****ing at 1.0 to 1.7 MPH. The motor ran perfect until this year. After a few hours of *****ing the motor just stalls. Will not start unless I use the priming bulb. After it starts it will run for a few minutes then quit. After a few stalling cycles the motor will idle high and it is very hard to get it to idle at a normal speed and then stalls out after a few minutes.

I also noticed that the spark plugs are fouled with black powdery carbon.

Help

[99yam40]

If pumping the primer bulb is needed,I would be looking at the fuel pump an /or air leaking into the fuel system(suction side)

[sullivans790]

Thanks
I will look at these item again. This one has me baffeled.

Could my electric choke be acting up?

[99yam40]

Thanks
I will look at these item again. This one has me baffeled.

Could my electric choke be acting up?

I do not think Pumping the primer bulb would help a choke

[sullivans790]

I seem to have two problems. one is stalling & two is fast idle. After it stalls a few times, I will start it up and it will run 2.5 mph at idle. Runs good but way too fast. only way I can get it to return to low idle is to run in neutral at high rpms for a few minutes.
The motor will run fine for a 10 to 15 minutes then stall out.
John

[sullivans790]

Just noticed that the spring is missing on the air adjusting screw...
what will that do?
Part number 647-14334-00-00

[99yam40]

the spring it there to keep the screw from turning all by itself changing the adjustment

[panasonic]

the spring it there to keep the screw from turning all by itself changing the adjustment

Which may have already happened...

[cleddau1]

Does sound like mixture is too rich. There has been discussion on this forum about the electrothermal fuel primer (called a starter set by Yamaha and not really a choke device). They are supposed to be reliable but everything fails eventually. Wondering whether they fail in the off/cold start position or the on/warm running position or any point in between? Is the warmth of a running engine enough to keep the wax melted and the needle in the warm running position even if the device itself has failed?

[panasonic]

Does sound like mixture is too rich. There has been discussion on this forum about the electrothermal fuel primer (called a starter set by Yamaha and not really a choke device). They are supposed to be reliable but everything fails eventually. Wondering whether they fail in the off/cold start position or the on/warm running position or any point in between? Is the warmth of a running engine enough to keep the wax melted and the needle in the warm running position even if the device itself has failed?

Prime start needle is retracted when the engine is cold allowing extra fuel through a passage in the carb to enrich the mixture and allowing the engine to start. As soon as the engine starts there is 12 volts applied to the prime start and the needle extends and closes off this passage slowly as the engine warms up.(If I remember correctly)

I suppose if this is stuck in the retracted position allowing extra fuel through...it would be like running the engine with the choke on.

Easy to test..remove the prime start from the carb and apply 12 v to it and the needle should extend and let it cool and needle should retract.

Check that there is 12 volts getting to the prime start when engine is running.



Could you supply the Serial number of the engine on the data plate? And the year if it is on it?

[sullivans790]

I cleaned the carb and reset air adjustment screw on idle for a smooth running engine. Tested for voltage at the prime start circuit. I did not measure 12 vdc when the engine was warm. I did measure 6 vac. looks like the leads to this primer start leads to the coil on the flywheel. Also noticed that the solenoid on the prime circuit was warm.
Any help on how this prime start circuit runs?

[boscoe99]

The electrical system provides AC voltage to the PrimeStart device whenever the motor is running. Voltage will be low at idle and increase with an increase in N. 1 below is the electrical generation coil and 2 is the PrimeStart device heater circuit.



The PrimeStart device is tested on a bench with 12 volts DC.

[sullivans790]

Thanks so much.
What is your source of information. I think I need some training/sources so I can learn and help others. Love to dig in but often don’t have the technical information.
Is there a technical manual for my 9.9 EXHY?
Thanks again.

[99yam40]

Yamaha sells service manuals
check with your local yamaha dealer for the proper manual # for your motor.
then by from them or find online