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  •  » FYI Ford, Classic Mustang Tech Discussion
  •  » Vacuum Advance

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    8/08/2020 6:36 AM  #1

    kardad
    I FYI 24-7

    Offline

    From: Lexington Ky
    Registered: 12/03/2019
    Posts: 305

    Vacuum Advance

    Trying to decide if I can see/fill any Benefits from running my vacuum advance, right now it is plugged off. Let me start by saying the car runs great, just always looking for that last tweak. My setup is:
    MSD 8479 Distributor
    Intitial timing 12 degrees
    Total timing 34 degrees
    All in by 2800 RPM
    Starts great.

    Now the issue, the MSD vacuum advance pot is not adjustable, and with the vacuum hooked up the timing will advance 40 plus degrees (off the scale). I haven’t driven it with the vacuum hooked up as that has to way to much.

     

    8/08/2020 5:04 PM  #2

    6sally6
    Hyper FYIFORD ADDICT

    Offline

    From: Surfside Beach,SC
    Registered: 4/02/2013
    Posts: 6,855

    Re: Vacuum Advance

    Keep in mind............at idle vacuum advance put A LOT of timing in. As soon as you crack the throttle it drops WAYYY off.
    That's why you can'y adjust vac. advance at idle in your driveway.
    Hook it up and try it!! Put it under a load and TRY to make it spark knock. IF it does you need to get an adjustable vac. pot and put it on your dizzy and adjust it that way.
    I don't have my vac. advance hooked up!!!!!
    If it ain't broke.......don't fix it.          If it screams now............what more do you want?!!
    6sally6

    Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
     

    8/08/2020 5:50 PM  #3

    RV6
    Senior 24-7 FYI Addict

    Offline

    From: Pine Junction, CO
    Registered: 3/01/2016
    Posts: 1,249

    Re: Vacuum Advance

    I checked out the instructions for your distributor and MSD says the vacuum only adds 10 degrees of timing. The 40 you speak of is is not right.
     

    Gary Zilik - Pine Junction, Colorado - 67 Coupe, 289-4V, T5
     

    8/08/2020 6:25 PM  #4

    kardad
    I FYI 24-7

    Offline

    From: Lexington Ky
    Registered: 12/03/2019
    Posts: 305

    Re: Vacuum Advance

    I guess the reason I’m fooling with it is I can’t seem to leave anything alone.

    The vacuum advance is hooked up to ported vacuum above the throttle plates, so at idle and the throttle plates closed there is no vacuum. The vacuum should come in as the plates open and under light load.

    My total timing without the vacuum advance is at 34 so if the vacuum advance adds 10 that is right on what I see when I hook it up and run the throttle up to 2500-3000 RPMs which is 40 plus.

    I haven’t driven it with the vacuum hooked up yet, I have to believe it will deadenate with that much advance.

    I haven’t opened up the distributor in quite a while but it seems like if the mechanical stop is at 34, how does the vacuum advance take it past that? I know there are different size bushings that limit the amount of advance.

       •Thread Starter
     

    8/08/2020 7:35 PM  #5

    6sally6
    Hyper FYIFORD ADDICT

    Offline

    From: Surfside Beach,SC
    Registered: 4/02/2013
    Posts: 6,855

    Re: Vacuum Advance

    IF its like a Duraspark (sorta!) the vacuum is hooked to a separate plate that advances/retards when vacuum is added.
    (Is the word VACUUM the only word with a double U?!....interesting)

    Just like............If a guy is really good at operating a Ditch Witch would he be considered a "master of Ditch-Witch-craft"?!
    Deep Thoughts......
    6sal6

    Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
     

     

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