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Thread: SU -dashpot bump spot dimensions ?

  1. #1
    Registered User germanz's Avatar
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    Default SU -dashpot bump stop dimensions ?

    Hello Folks,

    I have no real problem with my carbs, only that they are running a bit too rich on idle. A friend stated, that the pertinax dashpot bumper is worn and now the gap is too small. The result is that there is too much underpressure at the needle.
    I have the original factory manual and I have the ztherapy video, but nobody mentioned about the original dimensions. For a better understanding I made a picture.


    Does somebody know more about this little piece of plastic


    Thanks in advance Rainer
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    Last edited by germanz; 03-23-2005 at 09:05 AM.

  2. #2
    Registered User 240ZX's Avatar
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    Default

    Correct me if I'm wrong, but would this not create a leaner mixture because the needle would be seated deeper into the adjustable jet because of worn rubber stops? Maybe, just maybe, as the rubber bumpers wore down, the SUs were richened up to keep the idle high enough...hence causing a rich mixture at idle. Just a thought! Are the rubber stops, on both the SUs, at the same height? Are the oil levels and viscousity correct in the dash pots? Have you done the standard tune-up items and then syncronized the carbs?

  3. #3
    Registered User germanz's Avatar
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    Hello 240ZX,

    I believe that the influence of more under-pressure at the needle-seat is much bigger than a smaller needle opening. My carbs run ,fine only the emission test
    at idle is hard to reach.

    Both stops look like hammered flat. There might be a test with color tune spark-plug and lifting the dash pot, till the ideal position is found.

    At the moment I have 2/10mm I expect 3-4/10 mm will help.

    Cheers Rainer

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