vac leak?

Discussion in 'The Garage' started by alexgg, Nov 14, 2012.

  1. alexgg

    alexgg Been here awhile

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    Hi, I just installed new carby on bigger barrel. Tuned it up and everything seems to be fine within specs except - when I sharply close the throttle (two cables design) the revs gradually go to idle. I mean gradually: 3 -- 5 secs instead just comeback to 1.5k instantly. Cables are fine, carby jetted as most people do for my configuration. Anybody seen that weird behavior?
    #1
  2. Anorak

    Anorak Woolf Barnato

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    Lean idle mixture.
    #2
  3. alexgg

    alexgg Been here awhile

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    does it mean that pilot jet must go up size or two?
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  4. Anorak

    Anorak Woolf Barnato

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    Try the mixture screw first.
    #4
  5. alexgg

    alexgg Been here awhile

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    Hmmm if I play with mixture screw it will increase or decrease revs. At the moment I have 1.5k rpm on idle very stable. Mixture screw is 2.3 out after tuning. Originally it was at 2.5.. I was using Mikuni man to tune up mixture and idle screws. Going in and out to extremes of mix screw was killing the engine. Could you tell me exactly how to try.
    #5
  6. ParaMud

    ParaMud Been here awhile

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    What bike?


    Mainly posting so I can come back to this because my Girlfriend's klr is doing the same thing. I still need to drill out the idle screw to clean and check it.
    #6
  7. manic mechanic

    manic mechanic Been here awhile

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    Raise the idle speed to ~2500 RPM. Adjust the idle mixture screw until the RPM achieves a maximum, then back out the screw maybe 1/8th turn. Restore the idle speed to the desired level. Go for a ride and see how it does.
    #7
  8. VStromTom

    VStromTom Long timer

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    Check the vac hoses, my KLR did the same thing after I was careless pushing on the vac hose behind the shutoff, not all the way over the bulge. Also, sure you didn't pinch the diaphram or that is doesn't have a small hole in it?
    #8
  9. alexgg

    alexgg Been here awhile

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    Carby is TM36-68 pumper flat-slide. Bike KLX350 big bore. There are no vac hoses on this kind of carby coz it is not CV. I will try to retune at 2500rpm and see what gonna happens...
    #9
  10. ttpete

    ttpete Rectum Non Bustibus

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    You might check that there's no split in the rubber adapter between the carb and head. To check for vacuum leaks, use an unlit propane torch and go around anywhere a leak might be. RPM will change if a leak is found.
    #10
  11. alexgg

    alexgg Been here awhile

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    Thats smart idea... Something to have in mind for general knowledge!
    #11
  12. LuciferMutt

    LuciferMutt Rides slow bike slow

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    WD-40 works too but is messier.
    #12