I have a '72 with an LS5, Edelbrock 1411 carb, Torker II intake, headers, stock cam, and an HEI distributor. I'm currently running the Moroso advance curve kit with the lightest springs, and vacuum is 18 at 650 rpm.

With the car warm, and the vacuum advance disconnected, I put the distributor cap back on, started the car, and turned the dist until the vacuum peaked at 18. The timing light (adjustable) indicated that I already had 26 degrees advance at idle. In spite of that, I drove the car and it ran great. Pulled really hard, no pinging, and sounded about right.

I came back (it was idling steadily at 650), connected the vac advance line, and afterward, it would barely idle at all (rpm was also jumping around). I left it connected, adjusted the idle up to 650, then put the timing light back on it and it showed me 36 degrees advance (yes, at idle). The rpm was still jumping +-50ish. The vac advance is adjustable, and I tried all the way in, all the way out, and right in the middle, and it never improved in any of the 3 positions.

The car has never run better, but I'd prefer to have the vac advance connected (for fuel economy and temperature advantages).

Is 26 degrees too much advance for idle rpm? If so, and I rotate the distributor to reduce it, my vacuum (18) will fall, which would seem to be the opposite of what you'd want. Is it better just to set it all-in at 38 degrees and let the vacuum Hg fall where it falls?

Finally, is there a good all around vac advance (HEI) for a fairly stock street car?

 

set your timing at 2000-2500 with the vac adv disconnected, after that hook it back up then set your idle.

see how that works.

 

Standard Ignition offers a part # VC302 vacuum advance that fits HEI distributors that has 10 degrees of advance, it is the unit we use.

Henry @ olescarb