Idle problem with 1988 9.9 Yamaha

[Joe Batch]

I've had this motor since '88, bought it brand new. Nothing ever wrong. I last used it Jan '08, then did not use it until a month ago. A month ago, when I first used it this fall, it wouldn't start after many pulls. Took it into the Yamaha dealer. He cleaned the carb and re-gapped the spark plugs and "ran it in test tank and adjusted air mix and idle." When I got it back, it started up fine. But it idled fast and would not slow down on its own, as it used to do after about a 3-minute warmup. Turning the throttle back and forth had no effect. After 15 minutes of fast idle, I turned the motor off, turned it back on and the fast idle was gone -- I was then able to adjust the rpms to any level with the throttle. However, when I shut the motor off and took a 5-minute trip upriver using my main motor, the same fast idle problem occurred again when I re-started the 9.9. This happened repeatedly for two days

Also, there was a noticeable trail of oil and/or gas in the water from the motor the whole time, decreasing as time went on but still some there both days.

I took it back to the Yamaha mechanic. Picked it up today. His diagnosis: "oil level was too high, made the idle run too high. checked enrichener on carb -- it's working. on the gas and oil leak, pulled dipstick and gas and oil came out. drained out the oil, replaced the filter, put in new oil. let motor run in tank to see if motor is leaking gas to oil. motor runs good. checked the idle -- motor runs fine."

When I started it up today, again the idle was fast and would not decrease on its own. After 12 minutes of fast idle, I shut the motor off, re-started it and the idle returned to a slow idle. However, the motor runs faster than it used to at the lowest level on the throttle, making my boat go too fast to fish in real slow current, I could only fish in faster current. And again, there was a slight trail of oil/gas, not as much as before but noticeable.

What could be causing the fast idle not to decrease on its own within the normal time frame? And the oil and gas trail in the water? And the slightly faster rpm at the lowest throttle level after the fast idle goes away? I'm taking it back to the repairman tomorrow, but he doesn't seem to be able to correct the problem. Or does it run fine in his tank but not on my boat?

I have a system that automatically mixes gas and oil for both my 115 Yamaha and my 9.9. I connect the gas line only to the motor in use, switch it back and forth.

It's 1:30 in the morning. Will check back for responses tomorrow night after fishing and returning the motor to the mchanic.

Help. Thanks.

 

[sdsaw]

Re: Idle problem with 1988 9.9 Yamaha

While reading your post, I was assuming that you have a fourstoke until I reached the end, then you mention that you pre-mix you gas and oil on both the 9.9 and 115

Since you mention "oil level and dipstick" I'll go on the assumption that we're referring to a fourstroke 9.9 with the "Auto start carb system"
With this system, the engine temperature plays a very important role. You must have a properly functioning thermostat for the system to function correctly.
When it reaches the proper temp, it will disengage and your idle speed will drop.
It monitors head temperature and uses bi-metal valves which controls the vacuum lines to turn on and off.

-Check all the vacuum lines to make sure that they are connected and not leaking.
-Check the thermostat and go from there

The high oil level doesn't seem right.
You may have a leaking fuel pump diaphragm which is filling your crankcase with gasoline

As far as the idle speed being greater than before, your mechanic may have bumped it up when he worked on it last.
You can lower it back down to your liking.

Any more questions, just ask.
I've messed with mine quite a bit over the years

Scott

 

[JUSTINTIME]

Re: Idle problem with 1988 9.9 Yamaha

find a new tech
you need a new fuel pump or t stat is bad

 

[rodbolt]

Re: Idle problem with 1988 9.9 Yamaha

I tend to agree on the tech part but dissagree with the "just diddle with the idle speed part.
set it up CORRECTLY the first time and it tends to work exactly as desighned, ya just cant diddle with it.
the 85-94 auto enrichment system was rather tricky to properly set up and diagnose.
the carb passages are very tiny and sucseptible to contamination,especially if you recently switched to ethanol blended fuels like our area did in june 08.
F9.9 idle speed in N is 950 gearcase submerged and 850 in gear trolling boat unrestrained.
T and FT versions are1150 N and 1000 RPM in gear trolling hull unrestrained
any variation and its broke, get it fixed but you cannot randomly start making adjustments to make it any speed you wish.
but do check the fuel pump and the T stat and the actual cylinder/block operating temps. if they are low the enrichment system cannot compensate cause it doesnt know its bad.
bi-mettalic strips are rather stupid but will mostly work as designed, if the temp is low they keep the mixture very rich,as designed.
that poor strip cant tell if a T stat failed or a pump diaphram failed.
myself in my shop, first thing that would be done is a cylinder leak down test, NOT A COMPRESSION TEST.
then check spark for proper operation. if the first two pass then its on to a complete fuel system check.
by the time I am done its fixed.
the key is trying to break the system into its subsystems and understand how each subsystem affects the system.
there again, the auto enrichment circuit uses tempreture AND vacum to operate properly. a leaking valve,excessive leakage or an ign miss can affect the enrichment circuits as they dont know another subsystem failed they just do what they do.