Carburetor help, please

Discussion in 'The Garage' started by FreyZI, Aug 24, 2018.

  1. FreyZI

    FreyZI Adventurer

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    TTR 125 sat for quite a while at POs. Rebuilt carb. Runs, but idle doesn't want to stay set. I can adjust idle right to where I want it, but when I give it gas and then let go, it either idles faster or or is slow in shedding rpms. Spring for throttle wire seems fine. Any suggestions on where to look for gremlin.
    #1
  2. sieg

    sieg Wearing out tires......2 at a time, day after day.

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    Sounds like a vacuum leak or mis-adjusted air screw/fuel screw.
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  3. shovelstrokeed

    shovelstrokeed Long timer

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    First thing to make sure of is adequate slack in the main throttle cable. You should be able to find at least 1/16" of lift at the cable end atop the carb without any change in idle speed.
    Then make sure the slide is dropping all the way onto the idle stop. Then recheck the play in the cable.
    Slow return from a high idle is normally indicative of a lean condition. Try richening the idle mixture screw.
    If none of the above works, you probably have a minor air leak, if not at the boots it could be the throttle Butterly shaft or the slide itself is worn and leaking within the body.
    #3
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  4. concours

    concours WFO for 44 years

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    Nope.
    Your idle passages are clogged, and your idle screw is in enough to begin running on the needle.
    Clean it THOROUGHLY this time...
    #4
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  5. ohgood

    ohgood Just givver tha berries !!!

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    blast out all the passages with carb cleaner then air rinse and repeat a few dozen times. this is while fully disassembled.

    blast out all the Jets similarly. pull all the air/mix/idle access and do similarly.

    choke circuit too.

    all around the side/needle area also.

    it's not about having a positive flat bowl, but instead getting all the passages completely clear.

    when you think it's clean, put a pocket magnifying glass on it with a strong light and look again.
    #5
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  6. scratchypants

    scratchypants Loathes the impolite

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    Not shedding RPM's is usually a result of running lean. That can be caused by all previously mentioned conditions - dirt, vacuum leak, improper mixture settings. Anybody who has dealt with rebuilding carburetors has at one time said "I cleaned and rebuilt it - it must be something else" - this guy included. I'll add that not all carb rebuild kits are of equal quality. Spend the money on a reputably sourced kit, and do it again. Also, canned carb cleaner is no way to clean a carb (in case that's what you did) - you need to submerge it in a bucket of cleaner.
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  7. SnoDrtRider

    SnoDrtRider I've been lost here before...

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    I had a Honda XR 100 that I borrowed from a friend for my wife to practice riding on.
    It had a weird idle problem and I found that someone had the carb apart and put the needle in ABOVE the throttle cable retaining plate that sits on top of the slide below the return spring.
    The needle could float all over wherever it's happy self want to causing erratic idle issues.
    #7
  8. tominboise

    tominboise Long timer

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    I had a TTR125 with similar issues. I couldn't get mine started. I rebuilt the carb once and then the dealer rebuilt it and then when it still wouldn't start without a lot.of drama, it went down the road.
    #8
  9. FreyZI

    FreyZI Adventurer

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    Thanks for the thoughts, all. BTW, I completely disassembled and left it soak (overnight — got busy and temporarily forgot about it) in carb cleaner. It didn’t actually look that bad beforehand, except that PO had used some sticky goo in addition to the gasket for the float bowl. After the extended dip, I blew out all passages with compressed air. I will admit to using cheapest kit I could find on FleaBay.
    #9
  10. Tinker1980

    Tinker1980 Doesn't ask why, only asks how

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    I've found it helps to clean the jets with a strand of wire or even an old guitar string. Removing the jets, poking something through them, then spraying them out helps a lot.
    #10
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  11. spokester

    spokester Long timer

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    Also, don't rule out other basics like a tight valve or such.
    #11
  12. pvt joker

    pvt joker Latebird

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    There's a passage in the float bowl casting that is part of the idle circuit. It needs to be soaked, cleaned with a fine wire and blown out with hp air. You will always have problems if you don't get this passageway cleaned effectively.

    Or you can put on a new bowl - Nuke it from space, its the only way to be sure.
    #12
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  13. PeterW

    PeterW Long timer

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    Try cleaning it but there are occasions when I've just tossed carbs because nothing worked. (As above)
    #13
  14. squish

    squish Out of the office.

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    I had a XR250L
    I could not get the carb to work right.
    It wouldn't idle, but it would run fine off idle, or it would idle but then bog as soon as you lifted the slide.
    Then it started leaking,

    Damned thing drove me crazy, I swapped it to my buddy for the use of his trailer that his stores on his property.

    He ordered up an all new cleaning kit and float.
    It still wouldn't work. He even took it to a buddy who used an ultrasonic bath.
    Still wouldn't work.

    He gave up and bought a NOS or early take off stock carb, (or maybe a XR250R carb)
    And I shit you not, it bolted on and the bike ran perfect, one kick, no bog, perfect idle,
    He paid like $50 for the carb that between four of us had spent hours working on.

    TL/DR
    Try cleaning it one more time, or just buy a new carb and be done with it.
    #14
  15. JohnCW

    JohnCW Long timer

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    If you used anything from that kit other than just the gaskets ...... there's your problem.

    Go pull the jets, needle, and float valve or any other mechanical bits replaced out of the bin if you haven't emptied it yet, clean them up, and reuse. Assume NOTHING in that kit is either the correct size or of a suitable quality.
    #15
  16. Zuber

    Zuber Zoob

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    Very common on small hondas. Valves get tight and it will run lean, with a floating idle.
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  17. sieg

    sieg Wearing out tires......2 at a time, day after day.

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    Hmmm I can see a tight valve effecting fuel/air delivery and compression not fuel/air mixture, as in leaning the mixture. ?? How is this possible?
    #17
  18. shovelstrokeed

    shovelstrokeed Long timer

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    It isn't possible or even likely. A loss of pumping pressure is possible so compression ratio goes down, this could lead someone who is reading a plug to make an error. Reading plugs with oxygenated gas and zero lead is a useless exercise in today's world anyway. Wide band O2 sensors have made the need to read a plug more or less obsolete. Most people have no idea how to interpret a reading anyway.
    #18
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  19. sieg

    sieg Wearing out tires......2 at a time, day after day.

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    What he said.^
    #19
  20. fast1075

    fast1075 Fasterizer

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    Textbook plugged air bleeds. Trust me.
    #20