A nice vacuum advance article

[Ford428CJ]

Ported vacuum spot then. It should be below that and you might have to adjust your secondaries  open a little more so the primary butterflies sits below the ported vacuum port then. Still back to proper carb adjustment

[e philpott]

First paragraph states that lean requires longer to burn and more advance.  Lean burns quickly, and if it lights off too quick, you get a backfire.  I quit reading after that statement, and just glanced over the rest.  I don't agree with several things.  Joe-JDC

X2 ... you can even watch "burn time" with a ignition scope .... rich burns slow .... lean burns quick

[gordonr390]

I don't agree on the burn time analogy either. I run a 99% factory stock/original 69 S code and decided to change up the timing advance to manifold vacuum months ago. When I discovered my factory advance was leaking I picked up a Standard pn#VC31 unit to give it a try while I figured out where to send my factory unit for refurb. I set the max timing @ 36* and at idle it settled down to 22*.  Drivability dramatically changed for the better. The car definitely is no horsepower king but the engine liked it and became more of a joy to drive. Fuel has changed sense 1969 and by running 92 octane now I felt it was a no brainer to try. 

[My427stang]

I don't agree on the burn time analogy either. I run a 99% factory stock/original 69 S code and decided to change up the timing advance to manifold vacuum months ago. When I discovered my factory advance was leaking I picked up a Standard pn#VC31 unit to give it a try while I figured out where to send my factory unit for refurb. I set the max timing @ 36* and at idle it settled down to 22*.  Drivability dramatically changed for the better. The car definitely is no horsepower king but the engine liked it and became more of a joy to drive. Fuel has changed sense 1969 and by running 92 octane now I felt it was a no brainer to try.

If you are happy with what you have, then it's all good.  However, I would say that you'd likely be even happier with a mechanical curve that did almost the same thing at low RPM.  What happens with your setup is that if you drop the hammer, the advance goes away.  If you had a bit more initial, a quick curve, and ported you'd have the same part throttle effects and the proper curve would be present when you went to zero vacuum

That being said, I am sure it's better than the stock slow and late timing curve, so is it worth recurving on a stocker?  Maybe not, I would, but again, if you are happy, that's the key and my guess is that yours IS significantly better than the stock curve, especially part throttle and low RPM

[gordonr390]

I don't agree on the burn time analogy either. I run a 99% factory stock/original 69 S code and decided to change up the timing advance to manifold vacuum months ago. When I discovered my factory advance was leaking I picked up a Standard pn#VC31 unit to give it a try while I figured out where to send my factory unit for refurb. I set the max timing @ 36* and at idle it settled down to 22*.  Drivability dramatically changed for the better. The car definitely is no horsepower king but the engine liked it and became more of a joy to drive. Fuel has changed sense 1969 and by running 92 octane now I felt it was a no brainer to try.

If you are happy with what you have, then it's all good.  However, I would say that you'd likely be even happier with a mechanical curve that did almost the same thing at low RPM.  What happens with your setup is that if you drop the hammer, the advance goes away.  If you had a bit more initial, a quick curve, and ported you'd have the same part throttle effects and the proper curve would be present when you went to zero vacuum

That being said, I am sure it's better than the stock slow and late timing curve, so is it worth recurving on a stocker?  Maybe not, I would, but again, if you are happy, that's the key and my guess is that yours IS significantly better than the stock curve, especially part throttle and low RPM

I agree. By having an aggressive curve on initial with the mechanical and a ported vacuum advance bringing up the the big end it would have more power. But I believe this engine is finished by 4500 rpm and could be almost hobbyish to pursue. I have top end set setup in the pipeline and will be using the setup you are describing when I go to assembly.

[Ford428CJ]

Very well said Ross! I 100% agree with that.

[cjshaker]

Like most other things, it really depends on the combination and how it's used. Iron heads with less than ideal quench, a very mild cam and low octane gas, all used in a truck that's going to be lugged or used to pull heavy loads can stack the deck against being able to use a higher initial with ported vacuum. Sometimes you need that timing drop under load to stay out of pre-ignition.

I'd try it the way Ross said, but while keeping an ear out for any spark knock.

[fryedaddy]

im glad i read this,i didnt understand vacuum advance dist.

[falcongeorge]

Misinformation , I see this repeated from time to time 

He just got it off the HAMB. I am an active member on there, but getting your tech advice on there is like getting your political commentary from the National Enquirer...

[Dot Heton]

No I didn't get it from the H.A. M. B.

[C6AE]

That article has been going around for years...

I think more accurate information can be had at the corner bar.
Just walk in, sit down and order a beer then ask the person sitting next to you "What do you think about this?"!!!

[Drew Pojedinec]

I don't agree on the burn time analogy either. I run a 99% factory stock/original 69 S code and decided to change up the timing advance to manifold vacuum months ago. When I discovered my factory advance was leaking I picked up a Standard pn#VC31 unit to give it a try while I figured out where to send my factory unit for refurb. I set the max timing @ 36* and at idle it settled down to 22*.  Drivability dramatically changed for the better. The car definitely is no horsepower king but the engine liked it and became more of a joy to drive. Fuel has changed sense 1969 and by running 92 octane now I felt it was a no brainer to try.

Your example is kinda like the folks that have a totally 100% original and 110% worn out front end suspension that changes over to rack and pinion and than raves to everyone about how the original steering sucks.
Why not address the issue instead of tossing band aids?
Either way, good luck, sounds like a nice car.

[e philpott]

Burn time is easy to watch on a ignition scope , wether the engine likes more OR less timing at idle still doesn't change the fact that rich mixtures burn slow , I was not giving a opinion just the facts , which is same reason JDC disregarded the author of the timing story because he doesn't know what he is talking about early in his write up

[falcongeorge]

No I didn't get it from the H.A. M. B.

Its all good. Thought maybe you did because of the "timing" , someone started a "ported vs manifold vacuum" thread on there about a week ago, and a link to this article was posted almost immediately.

[TomP]

Why is it I see many more aftermarket vacuum advance distributors with a cap over the vacuum nipple than a hose? They pay extra to get that vacuum version.