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  #1  
Old 03-19-2007, 09:39 AM
billblack billblack is offline
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Default how to bench test vacuum advance.

I have my vacuum advance canister out and "on the bench"

If I apply vacumm (via hand vacuum pump), the arm will move.

The arm only moves when the vacuum is ~15 mm Hg. I.e. the vacuum builds and builds as I pump and then "pop", the arm suddenly moves.

Are they supposed to work like this or should the arm move gradually as vacuum is increased?

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Old 03-19-2007, 02:34 PM
dodger1 dodger1 is offline
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IIRC, the advance should be gradual and begin moving with less than 15", (6-8"?). Some Mopar vacuum advances have a set-screw adjustment inside the hose nipple (Allen key) to adjust spring tension, handy for cams that won't give 15" at cruise throttle where you want the vacuum advance to be all in.
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Old 03-21-2007, 09:36 AM
billblack billblack is offline
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Thanks, that's what I thought. Mine just won't budge until the vaccum gets to ~ 15 and then "pop" it moves all at once.

Can I buy just a vacuum advance? I don't know what kind of distributor I have.


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Old 03-21-2007, 02:06 PM
dodger1 dodger1 is offline
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Yep, NAPA website lists them for around $22. You'll need to describe the car, year, and engine as usual for parts store catalogs.
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Old 03-21-2007, 04:19 PM
billblack billblack is offline
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Thanks, That would be a crap shoot though: I don't know what kind of distributor the car has on it. I didn't build the car AND I don't have enough experience to know if it is a MP distributor or a Stock distributor or a Whoever distributor.
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Old 03-22-2007, 04:11 PM
dodger1 dodger1 is offline
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MP or stock would use the same physical vacuum can. Maybe take the distributor to your favorite parts store, or to a friendly MP dealer if you have one and go from there. The MP unit will have an adjustable diaphragm in it.
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