I'm having difficulty finding a vacuum advanced for my dizzy. The distributor is marked:C7AF-12127-AA. Below those number there is a second set of numbers: 7L13. When I went to order a new advance my numbers did not match any of the distributors listed in LMC nor Rock Auto. Any help will be greatly appreciated.

 

I think if you look at Dennis Carpenter on line catalog you might find what your looking for.

Is this what you have?
http://www.ebay.com/itm/Ford-390-Autolite-Distributor-C7AF-12127-AA-Galaxie-8-D1-/111533842204?pt=Vintage_Car_Truck_Parts_Accessories&hash=item19f7ef5f1c&vxp=mtr

 

One thing to keep in mind is whether your engine is stock?

Even if you find the correct part number it may not be correct for your application at this point, for example if you have a hotter camshaft installed.

Many vacuum cans are only going to start pulling advance in at around 15 in. of vacuum, BUT, about all the vacuum a modified motor will pull to begin with is maybe 10 or 11 in. This will cause problems with the advance "fluttering".

What you want to do is map out your distributor curve - initial and mechanical timing or total advance based on your particular application, and then decide what vac can you need. They will vary on both "when" they start to advance and "how much".

 

Well, I have a 390 bored .040 over, an "RV" cam and a 65 T-Bird intake. I have the choice of a Mallory double point mechanical advance and the factory. Many people complaint about points, but I don't mind. When the big solar flair hits we will be able to drive from car to car to fill up our tanks. Ok, really I feel nostalgic when I think of points and solid lifters.

 

Then, you don't want a stock vacuum can. How much vacuum are you pulling at idle? How hot is an RV cam? Next question would be are you planning on using manifold vacuum or not. With a hot cam, this may be necessary. There's a widely quoted article on vacuum advance by a retired GM engineer, while I disagree with his assertion that ported vacuum is solely a "smog era" device, he explains things real well. Here's part of it:

"Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam."

 

I might add that any tuning of the curve can only be done accurately with a hand held vacuum pump and a good timing light, preferably an adjustable or "dial back" style. I seem to remember from using factory specs that most stock FE cans do start coming in at around 5 inches of vacuum if that's any help.

 

The VC31 is pretty much it. I think you may be over thinking this one. The springs and weights set the advance curve. The vacuum advance pot is identical across the varieties.

 

I have had all 4 at different times. Single points, standard resistor. With dual points you need an extra resistor. Also if you check the dwell there is always some variation because of the mechanical movment, If you check the dwell with an electronic ignition there is no variation. I converted to Petronics with a MSD Blaster 2 coil and saw a marked improvment in idle and all around driving with fast starts. I later converted to Dura spark using the same coil and it really made a larger improvment, with that MSD coil that spark was the longest and brightest blue I have ever seen. Something to consider.

 

Also don't forget guys the factory 1 piece Dizzy Diaphragms were adjustable in the vacuum nipple. I am assuming the aftermarket ones are also. That's why they have that HEX shape to 'em. Stick a 1/8" or slightly smaller allen wrench in the vac nipple.

 

3/32nd (2.5 mm) seems to be the magic number. 12 turns clockwise is max advance. The amount of advance is adjustable, but not when it dials in, afaik.

 

Well. I do have a Pertronics conversion for my original so maybe, I'll go to NAPA and get a replacement vacuum advanced.

 

Before you buy just the vacuum advance I suggest you check your old Dizzy and make sure it's not worn out also. No sense in buying a new advance and installing it in a worn out Dizzy. Either the bushings the shaft spins around in or the breaker plate that the points and condensor mount too. If the points are still in there start it up and check the dwell reading. 30 degrees for a V8. Now rev it up to say 2000 RPM. The dwell should not differ any more than 2 degrees.

 

A reman dizzy includes a new vac can, too.

For the money a stock unit w/new bushings and such is probably the best bang for the buck around in terms of improving performance. I'm not poor but $400+ seemed a bit much on the Mallory type replacements. I run a Pertronix but if needed can reinstall points back in no problem. A Cardone 30-2808 was $52 w/core. It was already setup with light springs and "all in" by 3000.

 

I did the technical test of sucking on it and there was no resistance at all. No resistance what so ever.

 

That does make it bad but the Dizzy might be worn out or close to it also. Just sayin'.