Ported vrs Maniffold vacuum

[72CampSpecial]

So-- ive done tons of reading and im still not sure how to proceed. here is where im at.

'72 C20 w/350 3/4 ton.
I Rebuilt the Quadrajet (w/in last year)
Dropped a HEI in about 6 onths ago... from a '75 GMC.(dont have model #/serial #..i need to go take a pic)

eveything works.. i had the vacuum line from the HEI hooked to a manifold vacuum source for the last few months, but the truck seemed like it was working hard. Ran smooth, shifts great, but no umph.

I moved the vacuum line to a ported vacuum source today and the truck seems seems to have more "pep"

I set the idle to 8 on the balancer timing mark with the ported vauum source pluged then hooked up the vacuum line from the vacuum advance on the HEI..idle jumps up to 14-16 (since that is past the marks on the balancer its a guess)...and like i mentioned i cant bring the idle back down with the set screw since its all the way out..


Issue: i have the idle set screw all the way out and the truck is still idling high (after kicking down once its warmed up not on the High Idle setting). its not too teribly high...just higher than i think it should be.

All i have is a basic timing light and a vacuum gauge so i cant talk in specific RPM #'s.. my guess its idling around 900-1000ish in park and drops down to a good idle in drive 700 maybe??.

Am i doing something wrong?