Yamaha 25hp Idle Air Screw

[mwsmith818]

Hey guys. New to the forum. I have a 1994 25 hp, 2 hole 2 stroke Yamaha and I’m having trouble with the idle air mixture. First off, which way do I turn the screw to richen/lean? I’ve heard left to richen and right to lean, and I’ve also heard vice versa. Secondly, where should I start out at as far as turns out? I’ve heard anywhere from 1 1/4 to 2 turns out and I just want to be sure I’m starting out on the right path. Also, ANY tips you y’all have for tuning the air mixture by EAR would be great, as I am new to outboards and carb’d engines in general.

Thank you in advance!

[Jason2tpa]

Tons of info on this matter found by using the search function....use keyword "idle mix screw" or likewise. Here's one of threads...

https://www.yamahaoutboardparts.com/...1985-90hp-etlk

Below noted is pulled from ^^^ this link and authored by Boscoe....

It controls the amount of fuel (with some air mixed within to facilitate the flow of fuel) that is drawn into the carburetor. Turning the screw outwards opens a passageway and allows more fuel to flow. Turning the screw inwards does the opposite.


As far as where do you start.....If you have the service manual it will indicate spec turn out. If not maybe someone will chime in w/that info. That's your starting point, then adjust screws to fine tune.

[99yam40]

service manuals have all the specs and procedures.
do you have one for your motor that you are working on?
when working on something it is always a good idea to check to see where it was set before you started jacking with the settings

[mwsmith818]

I wish I did have a service manual guys… but sadly I don’t. That would’ve been the first place I looked.

[robert graham]

Best rule of thumb is “clockwise until lightly seated, then back it out about 1-1/4 to 2 turns”…..may vary some from motor to motor, according to the specs.