dist vacuum advance- timed port vs. full vacuum

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I thought I had this concept down way back when I was a wee lad but recently came across something that puzzled me.

Now, the only way that vacuum advance makes sense to me is if the port is "timed" so that it does not see vacuum signal at idle. Otherwise you have full vacuum advance at idle! Right?

I was working on a car last weekend that had a factory carburetor and only one vacuum port, which was NOT timed. It had full vacuum signal at idle and ramped down from there.

How does this work? Is it really designed to have all that extra advance at idle? Doesn't make sense to me.

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call FBO. he tells you to run full vac with his dist.

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Allegedly a benefit of using manifold vacuum is to get some advance at idle, rather than running a lot of initial in the distributor. 5* Initial + 15* vac advance at idle = 20* 'initial', versus 20* initial in the distributor, and maybe having issues with kickback on the starter, and/or needing a start retard.

As the throttle opens, manifold vacuum gradually goes to zero at WOT. Ported vacuum goes from zero at idle, to full vacuum with the throttle barely cracked, and down to zero at WOT. So both end up with vac advance where you want it (part throttle cruising), and no vac advance at WOT.

(well, not completely zero vacuum at WOT, but you know what I mean )

Any car set up and tuned properly should run just fine with either method.

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I use manifold vacuum at idle, run better and water temp is lower...

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call FBO. he tells you to run full vac with his dist.

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Ya, he tells you alot...most of which is total BS....

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call FBO. he tells you to run full vac with his dist.

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Ya, he tells you alot...most of which is total BS....

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i don't have any of his stuff but it seems a lot of guys are happy with his stuff.

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The best one he has told me on at least 2 differet occasions is that no way will a BB mopar make anymore power with more than 34 degrees of total timing. No way, waste of time, wont do a thing........