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Thread: Main jet on small single 4stroke

  1. #16
    Should Get Out More a_morti's Avatar
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    Default Re: Main jet on small single 4stroke


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    Maybe it's previously been run on an open exhaust and/or pod filter? The jetting was increased for that but forgot to return to stock when took the silly parts off?

    Not many other reasons to go that much bigger on the main jet than a pod filter.

  2. #17
    A Bit Bored mala's Avatar
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    Default Re: Main jet on small single 4stroke

    Sounds like overjetted so maybe go back to stock.
    Would explain the sooty plug.
    At high throttle openings the main jet is very dominant so needs to be right.

    ATB

  3. #18
    A Bit Bored
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    Default Re: Main jet on small single 4stroke

    Well, put in stock main jet #122.5, and no disernable change in performance! Haven't checked the plug yet.Might get a slightly more open air filter and go back to the #135. And then forget about it. Get myself a 80mph 250+.

  4. #19
    Should Get Out More maccecht's Avatar
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    Default Re: Main jet on small single 4stroke

    Questions you say the carb is clean? How long has it sat? The small drillings in the carb clog easily from the krap fuel we have these days and sitting for a few months is all it takes. Had similar issues to you on many bikes and 90% were solved by cleaning the carbs. Soaking in Coke overnight is my preferred method. Having a compressor is also a boon as you can them blow out all the orifices. Have you checked the float height is correct? What year is the bike? Do you have a manual? Eliminate all the easy things first.

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