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Thread: Intake Manifold Leakage

  1. #11
    Join Date
    Jan 2005
    Vancouver Island B.C.


    Quote Originally Posted by T. Cotten View Post
    "Perfect" vacuum isn't achieveable, Dewey!

    But we can produce the same differential with pressure, as one atmosphere is just shy of 15psi.
    So 15psi is overkill, but it will display, with bubbles, any and all possible places for a vacuum leak.

    Even though the motor will never draw extreme vacuum, a tiny leak can still cause grief, or at very least a loss of performance.

    Aye...and what I was getting at is this statement..."as the negitive pressure in the manifold increases and approaches -14.7 psi".

    Since it says -14.7 psi...which is gauge pressure...that would be near 0 psi absolute...which like you say isn't achievable.

    Like you say pressurizing to 15 psi is overkill as a manifold is highly unlikely to see 15 psid. I know the importance of manifold leaks as I had a piston fry on my Sportster 35 plus years ago because of an air leak.

  2. #12
    Join Date
    Jun 2001
    Central Illinois, USA


    Once upon a time....

    I had built had built a '39 OHV for an associate, and had become quite quite familiar with it, allowed to ride it often.
    It was subsequently sold to a fellow who would return it to me for spring maintenance.

    One year, he said it "ran fine", but it just didn't seem to me to jump like the scalded dog I remembered.

    So a bubble-test showed just a little blister of tiny foam bubbles upon one inlet nipple rivet that took fifteen seconds or so to form.
    I sealed it with my 'secret sauce', retuned, and the owner announced that it ran "like a brand new motorcycle!"
    This leak only robbed performance, but many burnt motors brought to me "ran fine".

    No two leaks behave the same, except those that prevent the machine from running at all.

    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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