Adjustable vacuum advance
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Postmaster
Joined: Jul 2003
Posts: 2,688
Likes: 4
From: Southern Oregon
Adjustable vacuum advance
I didnt know my vacuum advance was adjustable, but it is. Took the dist. to a friend's to check the advance curve on his Sun machine. When he took a look at what the vacuum advance did it was found excessive. We talked about it and the large amount of vacuum advance may be cutting into the mpgs. With the insertion of a small allen wrench into the nipple of the module, vacuum advance could be easily increased or decreased. He set it at 10 dist. degrees at a vacuum of 14.
Another thing happened about the same time. While he was on the Sun I was messing around with a parts dist. I took just in case extra pieces would be needed. Found that the dist. has aftermarket breaker plates riding on a full circle of ball bearings. Pretty slick for an old dist.
Another thing happened about the same time. While he was on the Sun I was messing around with a parts dist. I took just in case extra pieces would be needed. Found that the dist. has aftermarket breaker plates riding on a full circle of ball bearings. Pretty slick for an old dist.
Senior User
Joined: Sep 2004
Posts: 323
Likes: 3
From: m571.com/yblock
46: you are not adjusting the amount of advance by turning that allen screw, you are adjusting the rate.
What the screw does is change the tension on the spring inside the canister, so that you change the amount of advance you will get at a given amount of vacuum.
Check out this page:
AMOUNT
If you slide your mouse over the newer kind of advance canister, you will see how they describe using the allen wrench in the hose barb to adjust the rate of advance.
The pic next to it is the older kind, where you use shims to change the tension of the spring and adjust the rate. This seems harder to do, but being able to take the unit apart also allows you to change the spacer for a piece of tubing that you cut, so you can then also change the amount of advance. Here's a better pic of the inside of the older style:
OLDER STYLE
So by turning the screw, you will not change the maximum amount of advance the unit can provide. You will change the amount of advance at any given vacuum setting.
What the screw does is change the tension on the spring inside the canister, so that you change the amount of advance you will get at a given amount of vacuum.
Check out this page:
AMOUNT
If you slide your mouse over the newer kind of advance canister, you will see how they describe using the allen wrench in the hose barb to adjust the rate of advance.
The pic next to it is the older kind, where you use shims to change the tension of the spring and adjust the rate. This seems harder to do, but being able to take the unit apart also allows you to change the spacer for a piece of tubing that you cut, so you can then also change the amount of advance. Here's a better pic of the inside of the older style:
OLDER STYLE
So by turning the screw, you will not change the maximum amount of advance the unit can provide. You will change the amount of advance at any given vacuum setting.
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Postmaster
Joined: Jul 2003
Posts: 2,688
Likes: 4
From: Southern Oregon
Thankyou for the link, I have put it in the favorites list. My vacuum cannister is just like the newer aftermarket, so we actually decreased the rate. I expect that to limit max a blocking method of some sort could be had (havent read the whole text yet). But, if I or we are right and the amount of vacuum advance seen on the Sun at 18 vacuum was excessive thus firing the cylinder too far down at cruise, and then decreasing mileage, we are on the right track (whew).
Please be mindful that I struggle to understand distributor advance and engine effect.
Please be mindful that I struggle to understand distributor advance and engine effect.
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Postmaster
Joined: Jul 2003
Posts: 2,688
Likes: 4
From: Southern Oregon
Here is a picture of the ball bearing supported breaker plates from the bottom side, and the vacuum advance that was in use. Note the straight arm on the vacuum unit. Are replacements available because this one is shot, and it would be nice to get the dist. back together and operational. Everything I am familiar with has the curved arm.
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Postmaster
Joined: Jul 2003
Posts: 2,688
Likes: 4
From: Southern Oregon
I read Wild Bunch's site last night "Why do we need advance?" for about the 4th time. Each time it makes more sense. As an old supervisor from the past used to always say, about everything, "We're getting there".
Old School Hot Rodder
Joined: Feb 2006
Posts: 6,472
Likes: 11
From: Exmore, VA
46yblock, the early dual advance (centrifugal and vacuum) units Ford built had a factory ball bearing breaker plate. If you take the end off the advance (where the tube connects) there are shims, a spring, and a hollow sleeve. The spring was available in different strength, the shims allowed for fine tuning of the rate and the sleeve set the maximum advance by stopping the diaphram travel. Try a parts source that deals with restoration. The advance will probably fit 1957 to maybe 1959 V8 distributors, I had a couple of Lincoln 430 distributors like that. Look for the distributor number to help locate an advance for it. Good luck!
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Cargo Master
Joined: Sep 2007
Posts: 2,095
Likes: 2
From: Wahpeton ND
I had a port coming off the side of my holleys primary metering plate. I blocked it off and tapped off my manifold vaccum port underneeth. I belive it to be manifold vaccum anyways as it has a channel going to a spot bellow the throttle plate.
I have this setup wrong. So I have been underadvanced on the road? (The previous owner did also when he set up the 2bbl.) I just found out my distributor shaft bushings are bad and need a new dizzy anyways.
So block off this manifold port and tap my advance off the ported vaccum? Re-set my timing and I sould basicly pick up a few ponies and some milage?
Wow!
I have this setup wrong. So I have been underadvanced on the road? (The previous owner did also when he set up the 2bbl.) I just found out my distributor shaft bushings are bad and need a new dizzy anyways.
So block off this manifold port and tap my advance off the ported vaccum? Re-set my timing and I sould basicly pick up a few ponies and some milage?
Wow!
Last edited by flipklos; Sep 17, 2009 at 02:18 PM. Reason: oops
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Thread Starter
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Postmaster
Joined: Jul 2003
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Likes: 4
From: Southern Oregon
46yblock, the early dual advance (centrifugal and vacuum) units Ford built had a factory ball bearing breaker plate. If you take the end off the advance (where the tube connects) there are shims, a spring, and a hollow sleeve. The spring was available in different strength, the shims allowed for fine tuning of the rate and the sleeve set the maximum advance by stopping the diaphram travel. Try a parts source that deals with restoration. The advance will probably fit 1957 to maybe 1959 V8 distributors, I had a couple of Lincoln 430 distributors like that. Look for the distributor number to help locate an advance for it. Good luck!
Freshman User
Joined: Aug 2007
Posts: 38
Likes: 0
Here is a picture of the ball bearing supported breaker plates from the bottom side, and the vacuum advance that was in use. Note the straight arm on the vacuum unit. Are replacements available because this one is shot, and it would be nice to get the dist. back together and operational. Everything I am familiar with has the curved arm.
Thread Starter
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Postmaster
Joined: Jul 2003
Posts: 2,688
Likes: 4
From: Southern Oregon
That ball bearing breaker plate was introduced in 1957 when FoMoCo got away from the LoadOMatic distributors. Early '58 model FE's also used it. The ball bearings are notorious for making wear spots in the race which in turn made the timing erratic. I use to just mark the bearing before removing it from the distributor and clock it a given number of degrees when reinstalling it to give a new spot on the race for the bearings to ride on.
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