Ported vacuum and timed vacuum are the same thing.
Obtained from above the throttle blades.

Full time and manifold vacuum are the same thing.
Obtained from below the throttle blades.

Lots of advance at idle is good because it takes time to burn the lean idle mixture.
The great majority of engines will run hot in traffic or at idle on hot days - and cold ones as well - if the vacuum advance source vacuum is selected to ported vacuum.

Ported vacuum and manifold vacuum both retard the timing when the throttle is depressed.
It may help to view the vacuum advance cannister as a vacuum retard device.

Rpm controls the mechanical - or centrifugal timing - nothing else affects it.

Load controls the vacuum advance due to varying vacuum levels of the engine.
Except at idle when ported vacuum shows zero and manifold vacuum shows full vacuum - 17" - 19" with a stock or very mild cam - the vacuum levels of both ported and manifold vacuum follow each other fairly close.

Mechanical and vacuum advance systems overlap each other depending on engine load and rpm so as to give you the proper amount of advance for a particular situation.


When you time the engine the vacuum advance line should be disconnected and plugged at the distributor end . . . golf tees work great for this.
If you set total all-in timing with the vacuum advance line connected to manifold vacuum you'll be giving away a lot of horsepower.
Same thing is true with ported vacuum although to a lesser extent since it takes a bit of rpm to get ported vacuum up to full vacuum levels.