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  1. #1
    FEP Member 83glxdroptop's Avatar
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    Feb 2008
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    Default Distributor Vacuum Advance

    Hi All,
    My question is regarding the correct vacuum hose routing for a single diaphram distributor. The correct hose routing according to a vacuum diagram I found for my year and model (1983 3.8 V6 CA car) is a hose from the "S" port of the carb, to a "VACVV" on the air cleaner (see pictures), then from there to the vacuum port on the distributor.
    Here's the rub: With this set up I do not get proper advance after 3K rpm. I lose vacuum and power. If I connect the distributor directly to the "S" port I get full advance and vaccum at higher RPMS ( in other words, the engine runs like a champ with this set up).
    What is that VACVV for (emissions related I figure) and how does everone else set thier distributor up? Factory of modified?
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    Last edited by 83glxdroptop; 05-01-2011 at 01:13 PM. Reason: Add tags

  2. #2

    Default

    I have it goin straight to the carb. on both of my fords. 82GT & 79 f100

  3. #3

    Default

    Something wrong with this picture, or at least how I'm understanding it. Vacuum advance
    should never be providing any advance at WOT. It's completely a part-throttle thing.

    The vacuum vent valve on the air cleaner is a combination delay valve, and also vents the
    vacuum advance to the inside of the air cleaner when vacuum is not present on the carburetor
    "S" port. This is done to keep fuel vapor from degrading the vacuum advance diaphragm. The
    nipple closest to the air cleaner should go to the distributor, and the one on the backside
    of the valve should go to the carburetor.

    The line to the distributor should be open to atmosphere when there is no vacuum on the
    distributor port. When vacuum is applied to the distributor port, the vent should close, and
    then vacuum should bleed over to the distributor. The delay function is there to keep the
    vacuum advance from causing a surge when you're coming off the throttle.

    If the problem is part-throttle performance and driveability, then I'd test the VACVV to
    see that it functions the way it should. If this is more of a WOT concern, I would check
    the mechanical advance in the distributor to make sure it's not gummed up or worse.

    I would also check to make sure the crank balancer ring hasn't moved, and that the timing
    marks are still accurate.

    Generally speaking modifying is modifying, and fixing is fixing. Your car didn't have this
    problem when it was new, it shouldn't need to be modified to not have this problem now.
    Cheers,
    Jeff Cook

    '79 Mont StaWag, 5.0, 58K original miles ... '81 Futura Coupe, 3.3, 62K original miles ...
    '85 GT 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT CFI/AOD Vert ...
    '65 notch, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ... '68 Vert 307 4-speed...
    (And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune)

  4. #4
    FEP Member 83glxdroptop's Avatar
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    Feb 2008
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    Default

    JACook, I agree and I think I need to review all vacuum haose routings again. As far as the VACVV, if I do need to replace I'm in trouble. I have looked all over the web for this item and cannot find one that looks like what I have in the car (not even sure if the item in my pic is original or even correct). I do prefer to fix back to factory OEM. The distributor is new actually and the balancer wheel is corectly installed (I did this my self during a rebuild).

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