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2018 yz 125 jetting help

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I have read my service manual quite a few times before i would come ask for help.. im not slow like that.. and it has regular charts and regular things to describe what main jet, pilot or needle you need but nothing too in depth.. thats why people come here to ask questions and as you said the fine tuning ive done to the air screw has no effect on the main jet but effects idle/ off idle where my problem is.. ive went through the procceses and everythings really right on the jetting for right now. When summer comes ill have to lean it out but why mess with the main jet and everything else if it has no effect on the airscrew/ pilot which like you said, is where my problem is.. ive paid very much attention to every thing above and read my manual.. neither points me in the right direction of my idling problem

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Okay lets go thru this again,

 

-set the air screw to it's nominal setting, 2-1/4 turns out

-warm up the engine thoroughly, ride the bike for 20 minutes or so making sure it's cleared out

-adjust the air screw to obtain the highest idle speed, if necessary (but usually not likely) re-adjust the idle screw if idling too fast

(see note at bottom)

 

If after that the engine bogs (lean) or stutters (rich) anywhere past 1/4 throttle, it is not air screw related

but rather the needle (1/4 to 3/4 throttle) or main jet (3/4 to full throttle) circuits than need adjustment.

 

Note: the air screw has a limited range of adjustment, more than 1 turn in/out from the nominal 2-1/4 turns requires changing the pilot jet size.    

Say in cold weather the engine runs better with the air screw turned in at 1-1/4 (meaning less air / richer mixture),

you then switch to one size richer pilot jet and to re-set the air screw back to it's nominal setting and repeat the 'highest idle' procedure.

Edited by mlatour

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Like Maltour said the air screw is not doing anything for wide open throttle.   Also let the bike get warmed up before adjusting air screw and idle.   Trying to set the idle cold will most likely have your bike stalling when totally warmed up.   If you haven't marked our grip or he 1/4 throttle increments ou should.  It might help you dial when you are getting the lean bog.  If you don't have a manual download it from the internet.  Great info o read.   

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