# Idle mixture screw adjustment on 20hp Yama!



## Bcomp866 (Mar 1, 2021)

I have a 2008 F20ESH Yamaha 4 stroke. I just got my carb cleaned and it runs great at WOT but is sometimes harder to start than it was last fall. When I got the boat back, I noticed the little brass plate that covers the screw was removed and they adjusted the idle mixture screw. I am an idiot and decided to play with it but don’t remember where it was. I have looked up the technique for adjusting and fine tuning but wanted to know where it should be to start. I’d also like to know around how many turns out they should be once adjusted. I currently have the screw 1.25 turns out, and it runs well especially at WOT. I also have started it a few times and seems to fire right up now! I want to be sure I am not making the engine too lean and am going to burn something up! Thank you for your help!


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## ek02 (May 8, 2012)

The factory setting is about 1.25 turns out. That screw only affects the idle circuit. Above idle it runs off the fixed size jets. It has no affect on WOT.


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## Bcomp866 (Mar 1, 2021)

Thank you for replying. This makes sense since it runs good at WOT regardless. I haven’t had time to get it on the water since tuning it last. But I do currently have the screw turned out approximately 1.25 turns. Thanks for your help


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