XR100 Problem

Discussion in 'Thumpers' started by clang, May 25, 2007.

  1. clang

    clang Not lost, Exploring!

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    Sep 18, 2003
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    2,805
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    Denver/Aspen
    OK, so I bought an old XR100 to get in on the miniTT races that Geek is posting about. It had been sitting for about 18 months (started a couple of times a year), but fired right up after about eight kicks.

    These bikes have a two position choke. When it is choked, it fires right up and runs well, when it warms up you can move it to the 1/2 choke position and it still idles well but it starts to stutter at high rpms. If you turn the choke off, it just dies, even when warm.

    I've drained the gas and carb, and tried fresh gas, I have pulled the carb and cleaned the main jet, the needle jet, the slow jet and the pilot screw. I put everything back together, readjusted the carb, and get about the same results. It idles better with the choke in 1/2 position, but still boggs at high rmps and dies when you trun the choke off.

    I'm going to get a rebuild kit tomorrow, is there anything else I should be looking at? Do these bikes have any quirks around carburetor adjustment I should be aware of???? Do I need a whole rebuild kit, or just new jets?


    Thanks :freaky
    #1
  2. experiment70

    experiment70 Been here awhile

    Joined:
    Apr 5, 2004
    Oddometer:
    274
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    Boulder, CO
    Forgive me if you already know all this...

    If this happens predominantly at idle, it might be an air screw problem. Where is your air screw set? If the bike likes choke, it's too lean. I'm pretty sure the XR100 has an air, not a fuel, screw (you can tell by where the screw is located - air box side = air screw, intake manifold side = fuel screw). Try turning the screw in, to richen the idle mix.

    To tune it, once the bike is warm, I set the idle screw a little too high, and then mess with the air screw until I find the spot where the bikes idles the highest. Then I reset the idle screw to a more reasonable idle.

    If this works, but the bike bogs when you whack the throttle open, try pulling the needle jet up one clip position.
    #2
  3. clang

    clang Not lost, Exploring!

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    Thanks :freaky

    I'm going to tinker some more tomorrow and see what happens :evil
    #3
  4. bykpimp

    bykpimp Live and let ride

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    Oct 18, 2006
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    Santa Cruz Ca
    Float bowl level, needle valve worn or a piece of debris in it??????????
    #4
  5. Hunsta

    Hunsta Have guns will hunt

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    Ditto on the float bowl level. Check for needle valve wear on one side. Will be very slight but noticable.
    Cheers
    Craig
    #5
  6. Eurobiker

    Eurobiker Vintage Cat Herder

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    I suspect this is the smaller version of the Kehin carb that's on my XR600. Try setting the pilot screw at 2.5 turns.

    [​IMG]
    #6
  7. woody's wheel works

    woody's wheel works Built to Last

    Joined:
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    FYI,,,,as a fellow advrider,,,be forewarned to keep your rear spokes tight,,check them for looseness OFTEN,,,,these rear wheels have a propensity to come apart at an abnormally high rate,,,especially when ridden hard.

    if you get tired of jerking around doing that,,,there is a solution,,,,basically changing from the x2 to a x3 lace pattern,,,that solves it:thumb
    #7
  8. wickedsprint

    wickedsprint Banned

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    You might also have an air leak in your carb boot. That would also give those symptoms, especially if it was a hair lean on top to dtart, that extra air would toss it into not being able to run at all.
    #8
  9. clang

    clang Not lost, Exploring!

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    Location:
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    Thanks everyone for the advice. Bike is now running well :clap

    A little fine tuning and we are good to go
    :freaky
    #9
  10. KneeKicker

    KneeKicker Long timer

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    Jul 26, 2006
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    I bought one last year with the same situation bike had basically set for 2 yrs the guy who had it strted every once in a great while just let it idle and shut it off. The jets didn't look bad but those little things are so small on the 100's that it doesn't take much i cleaned them and it would run fine but if it sat more than a week or so it ran like crap had to clean the jets and it was fine. I read some things on thumpertalk and decided to rejet the bike. It starts easyand runs better,I did add an FMF pipe and opened up the air box
    #10