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Thread: Thumb throttle with dirtbike carb issues

  1. #1
    Join Date
    Jan 2006
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    Ossian, Indiana
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    Thumb throttle with dirtbike carb issues

    Has anyone experienced any issues with the carb keeping up with the thumb lever. The guy tuning my quad said that the thumb throttle has too fast of a turn and that the accelerator pump can't keep up. It's an 05 wr250f motor with a older 426 carb on it.
    Thanks,
    Lonnie

  2. #2
    Join Date
    Jan 2006
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    Ossian, Indiana
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    I don't know what the issue was with my old carb but I put the original wr250f carb on it and added a quickshot to it and now it runs great no bog no stumble.

  3. #3
    Join Date
    Apr 2008
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    W.P.B. FL
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    Thats a jetting issue not a accelerator pump issue.

    You need bigger jets....trust me.

    They have huge lectron carbs on 4 strokes with no accelerator pump, if its bogging out from throttle stab you need more pilot, more needle and more main jet.

    Theres a lil wright up here on accelerator pumps http://www.jetsrus.com/FAQs/FAQ_reje...w_to_rejet.htm if you scroll down the page to "the process in detail" you can tune your quad with out the guy that says the "throttle" lol is causing the problem......thats to funny.

    Bog and stumble are deffinetely signs of lean conditions.

    Fire your tuning guy asap!!!
    400ex hybrid Finished!
    http://www.youtube.com/watch?v=YMDIAw8UskQ

  4. #4
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    Jan 2006
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    Ossian, Indiana
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    Thanks he isn't my tuning guy I was givin his name at the track, live and learn I guess. The main was a little lean, I went up 3 sizes and didn't see any change except that the plug looked better,it fires right up and idles like it should but when you stab it it bogs and when I try to ride it like a 2-stroke it blubbers all over itself so I'm thinking I need to try a different needle but I'm not sure how big to go and I don't really know the size or year of the carb the guy I bought it from had it on his 426 but the guy that was trying to tune it said its an older 400 carb how do I tell what it is. But since s running great now I'm not in any real hurry but I would like to get the bigger one right.

  5. #5
    Join Date
    Apr 2008
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    W.P.B. FL
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    2-3 jet sizes isnt even worth doing, unless your going in incriments of 5 like 160-165-170. Going 160-161-162 is a waste of time.

    You need to start off LARGE on jets, go big until it wont fully rev out and sounds like the rev limiter is hitting, then back down until it stops stuttering and fully revs out. "reccomended by the biggest jet supplier in the world" and truly the only way to tune a carb.

    Truthfully the pilot isnt a big deal if your quad starts right up without choke and doesnt pop and backfire on deceleration. Having a large proper main jet will make all the difference in the world, without a dyno to tune your quad the method in the link i provided and in the description above is the best way.
    400ex hybrid Finished!
    http://www.youtube.com/watch?v=YMDIAw8UskQ

  6. #6
    Join Date
    Jan 2006
    Location
    Ossian, Indiana
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    Okay thanks for all your help. How do I adjust the air/fuel screw with the carb on the quad.

  7. #7
    Join Date
    Apr 2008
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    W.P.B. FL
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    loosen up the mounting points on the carb, turn it sideways until the adjustment screw is visible, adjust it, tighten back up and test ride it.

    three turns out is were i generally put it, anything past 3 turns and still poping on decel and backfiring a bigger pilot is needed.
    400ex hybrid Finished!
    http://www.youtube.com/watch?v=YMDIAw8UskQ

  8. #8
    Join Date
    Jan 2006
    Location
    Ossian, Indiana
    Posts
    140
    Thanks

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