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2T jetting question.... we all love em

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  • 2T jetting question.... we all love em

    The bike is a 04 yz125, and ive recently changed from 40:1 to 50:1, using castrol tts.

    my maths is fuct so i cant work the % difference for the extra fuel its getting, in my head i see 20% more fuel but thats wrong, right?

    now the plug is showing richness, not like before when the plug was nicely tanned. pls note this was when the weather was still cool a few weeks ago.
    it now runs fine but crackley on part throttle deceleration. so im thinking, can i just lean the pilot screw, and more so, drop the jet needle 1 clip?

    this is more a lazy was of striking conversation than getting out there and doing it, which i will anyway. its good to be on the right track.

    any thoughts? maybe i should buy a smaller main jet to help with the summer heat also.

    awaiting your swift, knowledgeable replies

    smitto
    Lost and on reserve

  • #2
    use more oil....

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    • #3
      Hey dude, warm the bike up with a good flogging. Then set it to idle and then slowly wind the idle mixture screw in until the revs drop and then count the turns out until the revs drop off again. Turn the mixture screw to the mid point or fastest and best idle speed then shut the motor off. Count the turns in to closed on the mixture screw. More than 3 turns means your bike is rich and needs the next smallest size pilot. Less than 1 turn out means the bike is lean and you need to go up on the pilot. Ideal range for an air screw (2 stroke) is between 1.5 to 3 turns out. You can usually rotate the carb enough to get the bowl off trail side to change jets so I would just go down 1 size on the pilot and then ride it. Also, chuck a brand new spark plug in it and then run it at full throttle for as long as you're game (needs to be about 15 to 20 seconds). Then rip the plug out and check it. Should be dry and with light tan rings down inside the electrode. You can easily change main jets trail side by pulling off the carb drain, not the entire bowl. It's better to be slightly rich than slightly lean and YZ's aren't known to be fussy on the jetting.
      Paul

      Stuff the two strokes. Joined the four stroke club.

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      • #4
        I agree with Paul try next size down pilot if still spitting slowing down then as you said lower needle 1 clip.

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