'Ported' vaccuum advance is a product of the emmission laws, before the later '60s all vaccuum advance was full manifold vaccuum, either taken from the intake manifold or a carb port on the engine side of the butterfly.
The ported vaccuum is to defeat the vaccuum advance at idle, this, along with retarding the initial mechanical timing was supposed to lower the combustion temperatures, thus lowering NOX production.
For those from California that are old enough to remember the 'NOX Device' mandate for pre '66 cars when the smog checks started (this entailed disconnecting and plugging the vaccuum advance, retarding the timing, and putting a 'NOX' decal on the air cleaner) you know about the crappy running, overheating, and other problems this caused. The mod usually lasted long enough for an inspection then was put back to normal by the owner.
That being said... Snowman, if you are not going to fix your curb idle solenoid, you can rig a throttle stop the same height as the solenoid would be when extended, then your butterfly will be correctly aligned in the venturi (after backing off your curb idle screw and setting it correctly of course) then your mixture screw should be back to normal function.
I am a believer in full manifold vaccuum advance and running as much initial advance (like 10-12 degrees) as makes the engine happy, however, the smog carbs are jetted and calibrated for ported vaccuum so that is what you should probably do.
I have been working on cars for over 50 years, all I can say is this is what has worked for me.
Tim
