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Old 07-13-2010, 11:25 PM
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cobalt327 cobalt327 is offline
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Originally Posted by kyle86
That's not the problem. I've already disassembled the distributor, welded up and ground my advance slots 3 times already. I got the initial and mechanical timing dead on it's nuts. We think the problem is the vacuum advance isn't dropping out soon enough causing it to ping when I lightly tip in the throttle. Custom10 pointed out in an above post that the adjuster plate I made for my vacuum advance is limiting the advance from the wrong side. I made another limiter to mount on the opposite side same as the crane one that I'm going to try tomorow.
At light throttle cruise, the vacuum is as high as it is going to get. There's no way to lower the vacuum, or to set the vacuum advance to not be fully advanced at the maximum amount of vacuum that it will ever see, short of at idle. This is going to be the case, no matter what side the limiter is on.

The difference in where the limiter is (in front or behind like the Crane), has NO effect on how much vacuum it takes to first move the vacuum advance rod on the can I'm testing right now. Intuitively it may seem that it would be otherwise, but for that to be the case, the spring inside the vacuum advance can would have to be a progressively wound spring.

At least in the case of the can I just tested, this is not the case- but the real test would be on the one that you're using. What MY cans do or don't do won't help you either way, other than to see if there's a trend. So before assuming anything- check your can w/a MityVac like I just did. My can's marked AR16, BTW.

On my can, the same amount of vacuum causes the initial movement of the rod. Same amount of vacuum to begin the decrease of advance. This is whether the rod has had 1/2 of its travel taken up by a spacer placed in front or behind the rod. The same ~4 in/HG moves the rod, either way.

If there's a reason to, I have numerous vacuum advance cans out in the shop that I will be happy to test tomorrow to see whether they behave the same or not.

In any event, I believe if limiting the total vacuum advance amount that the can is set to provide doesn't do it- then nothing involving the vacuum advance will do it, period.

Last edited by cobalt327; 07-13-2010 at 11:59 PM.
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