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fuel screw question

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this is my first time installing an adjustable fuel screw and i would like to know if adjusting the fuel screw can help fix minor jetting problems? for example, if i cut a couple of small holes in the air box and/or install or remove a 96 db tip for the exhaust on my bike, can adjusting the fuel screw be an alternative to making very minor jetting changes?

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You would just have to test and see, fuel screw has a range in which it will adjust for proper pilot circuit mixture. If you go out of this range, a pilot jet change is warranted, whether up or down, depending where the fuel screw is negated. Each bike has a different spot where it is optimum(turns out on the screw), and this varies between identical models!!! So with the mods you are planning on doing, one sounds like it will give more air, making your system leaner(slightly) and the other will make your system slightly richer. Test, test, test...

Keep us posted.

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ok i think i might have overtightened the stock fuel screw a little bit when i was recording how many turns out the factory setting is. can this damage anything in the carburetor?

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As long as you didn't over tighten it bad you are fine. also on the stock fuel screw there is a tiny O ring, did you put that on the adjustable one? (its what keeps the fuel screw from turning from vibration)

Also the fuel screw adjust only a very small part of the throttle (like 1/-1/4) but has a very profound effect on how the bike feels jetted, since you always go thru that range with every twist

When i had my 06 YZ250f the jetting was VERY FINICKY and when every it got cool and rainy (basically whenever it got shitty outside) the bike would run horrible, it would bog/should flames/not rev

so i waould sit on the line and twist the fuel screw a 1/2 turn at a time until i found a spot where i could snap the throttle wide open with no bog ( i would often go both ways of adjustment until i found the perfect spot)

Basically yes the fuel screw will make minor jetting changes (as small of area that it works at it has a profound on how the bike runs)

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yep i put that o-ring on there. it's about 2 7/8 turns out right now, and the stock setting was 2 3/4 turns. and i know 3 turns is too many. seems to be running good so far

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Go 1 size larger on the PJ. Try to shoot for 1.5 - 2.0 turns open on the fuelscrew. The YZ should pop a little on decel, so try to avoid setting the fuel screw too rich. :thumbsup:

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