Mariner 90 HP IDLES TO HIGH

[hail2dskins]

First Post. I have a Mariner 90 HP, oil injected outboard, I believe it is a 1988. Just recently purchased this and more times than not it idles very high in neutral. It idles so high that it bangs into gear when I put it in forward or reverse. It also will not go slow enough in no wake areas. I have been yelled at several time now. Oddly enough on a couple of occasions it has idled perfect and goes into gear smooth as can be and will idle nice and slow in no wake areas. I have had the boat out a dozen times or so and 99% of the time it idles way to high? Any suggestions on what this could be and why would it fluctuate? One other thing I know this boat was not used for a couple of years before I purchased. I have read several cases where possible bad fuel can cause low idle, but could it also be part of my problem? Could some sea foam be a possible fix? Thanks for the help!

 

[Chris1956]

The combination of the adjustment of the throttle cable and the idle stop screw controls the idle speed. I would disconnect the throttle cable at the motor and adjust it to push the throttle closed, with some preload. If that does not slow the motor down, you will need to find the idle stop screw and turn it out a turn or two, and then adjust the throttle cable, if necessary. The idle stop screw is usually located next to where the throttle cable attaches to the throttle arm of the motor.

 

[hail2dskins]

The combination of the adjustment of the throttle cable and the idle stop screw controls the idle speed. I would disconnect the throttle cable at the motor and adjust it to push the throttle closed, with some preload. If that does not slow the motor down, you will need to find the idle stop screw and turn it out a turn or two, and then adjust the throttle cable, if necessary. The idle stop screw is usually located next to where the throttle cable attaches to the throttle arm of the motor.

I looked last night and this motor has three carburetors. Does it have one idle screw that adjusts all three carbs, or do I have to adjust each carb individually?

 

[DavidMoore]

No Title

You do not adjust the carbs, those screws are for mixture setting only.

To adjust the idle speed you adjust low speed the ignition timing, see sketch below. for the correct screw to turn. Engine should idle about 675 rpm.
It 's important you do this with the boat in the water and the engine at idle in fwd gear.

If you messed with the screws, turn them in until lightly seated, then back them out 1 1/2 turns. This will put you in the ball park of where they should be, you can tweak them later by opening / closing them by a tiny amount (width of a screwdriver blade) in order to get best acceleration.

 

[DavidMoore]

No Title

Sorry
That photo is a 4 cyl. Try this one should look like you have.

 

[hail2dskins]

Sorry
That photo is a 4 cyl. Try this one should look like you have.

Thanks for the sketch.

 

[alanfox55]

I have a 97 two cyl 30 hp that would not idle below 1600 rpm. I cleaned the carb twice and rebuilt, did link and sync,tried to adjust idle screw and mixture screw but when I adjusted below 1600 it would die. Then I soaked it in Yamaha carb cleaner for eight hours,sprayed and blew it out and that worked. The idle dropped to 1100 rpm then with the idle and mixture screws was able to get it to 850 on muffs with no problem. When I put it in the lake it dropped to 700 in gear with a light boat.

https://youtu.be/Y9UlIezKTVo

 

[hail2dskins]

Sorry
That photo is a 4 cyl. Try this one should look like you have.

DavidMoore I wanted to thank you for your help. I was able to use your sketch and turn the idle down on my motor. I took it out last evening and it ran spectacular. Thanks again!

 

[DavidMoore]

Brilliant, thanks for the feedback.
Happy boating