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vaccum Advance Module

Discussion in 'The Garage' started by Justin Fleming, Sep 11, 2005.

  1. Justin Fleming

    Justin Fleming 1/2 ton status Premium Member

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    How does the vaccum advance work. I though in the past that when setting the timing you unhook it and set base timing. when pluged in the timing would advance quite a bit. mine seems to only advance a few degrees. I also unhooked the vaccum line and sucked in on it to see if a could here a diaphram movement noise and i didnt hear anything. :confused: :rolleyes: :rolleyes:
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Vac advance like yours is hooked to "ported" or "timed" vacuum. As you increase throttle opening, it will uncover a slot in the praimry wall that then "sees" engine vacuum, which will pull advance.

    Manifold or unported vacuum is what you are thinking of that pulls full manifold vacuum at idle.

    You are still supposed to pull the vac advance when setting timing, as obviously those 3* is a fair amount if talking 8* base timing.
     
  3. Justin Fleming

    Justin Fleming 1/2 ton status Premium Member

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    I have it hooked to manifold vaccum. The truck base timing calls for 4* witch seems very little. If I suck on the diaphram should I here it move and function?
     
  4. diesel4me

    diesel4me 1 ton status Premium Member

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    try this...

    Sucking on the vacuum advance hose SHOULD make it move--a quicker test is to just remove the hose from its manifold vacuum source,and plug the nipple--engine idle speed will decrease with no vacuum,which = no advance..plugging it back on will increase idle speed if the vacuum advance is working..

    Thats how I test vacuum advances with ported vacuum too--i swap the hose to a manifold vacuum source,if the motor speeds up,its diaphram is ok.. :crazy: --a tester like a "mightyvac" will show a diaphram with "slow leaks" better..it applies vacuum via a pump,and you can watch and see if it holds vacuum for a length of time without dropping..you can do the same with your tounge once you know how to do it!.. :crazy:
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    3* with manifold vacuum means something is wrong. It's either ported, or the advance can is leaking.
     

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