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Thread: Quadrajet question

  1. #1
    Learner Driver
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    Quadrajet question

    Hi Team. Just wondering what this part of my quadrajet is. What does the hose attach to and do I need it. It has been disconnected for the last 20 years.

    quaddie.jpg

    Cheers,

    Max

  2. #2
    Cruiser axistr's Avatar
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    This vacuum servo is designed to lock out the vacuum secondaries at low manifold vacuum, (during low engine RPM). If the secondaries open to early the engine will run rich and bog down until the engine gains RPM and a higher inlet manifold vacuum. The secondaries will open only a minimal amount at full throttle until the servo has enough vacuum to pull the leaver and unlock the secondaries so they can open 100%.

  3. #3
    Learner Driver
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    Thanks Lenny.
    So it should be connected to any manifold vacuum source - not ported?
    Cheers,
    Max

  4. #4
    Cruiser axistr's Avatar
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    Memory not as good as it used to be Max, but I think they may have been connected to ported vacuum. Might pay to find a vacuum plumbing diagram for the intended model.

  5. #5
    Night Rider Innuendo's Avatar
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    Best I can remember is that BS didn't happen until WB and Commodore. HZ didn't have it.
    If you can show me pictures on the stamped numbers on the drivers side of the carby I can decode for you.
    Selling HJ 253 Engine
    Engine Number QR718*** | 19M5 Clock Casting at 6 O'Clock
    19th December 1975 Suit HJ Late Dec 1975 to April 1976

  6. #6
    Cruiser axistr's Avatar
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    Thinking about the vacuum connection a bit more, it would have to be connected to a vacuum port that doesn't have direct constant inlet manifold vacuum, or the servo would unlock the secondaries at idle which has a high vacuum situation. The vacuum hose would most likely be connected to a port on the carby. I think all Q-jets had this feature regardless of year and series. Yep Inners is right, Carbys from HZ or WB onwards would have more vacuum ports on the carby and manifold for the start of all the extra pollution regs. HX had some extra pollution bits but also started robbing power with retarding the cam timing.

  7. #7
    Night Rider Innuendo's Avatar
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    quadrajet_vacuum_bs.jpg

    There is all you need to know about the vacuum bs via air cleaner
    Selling HJ 253 Engine
    Engine Number QR718*** | 19M5 Clock Casting at 6 O'Clock
    19th December 1975 Suit HJ Late Dec 1975 to April 1976

  8. #8
    Learner Driver
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    Thanks Night rider. My Carby was off a WB 253 that I've had rebuilt to suit my 308. The one in the picture was just one I found online.

    - - - Updated - - -

    Cool. Thanks again Len. My carby has plenty of spare vacuum ports I can use.

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