Dist. vacuum advance, retard, ported, manifold?, Anybody know the real story? Options

[JPA914]

I'd like to test the vacuum canister on my 1974 2.0. It just has the one line going to the TB, the other vacuum port is open to the atmosphere. TB has only one port, the other is blocked off for my year model. Now, from all I've heard, this is a retard ONLY setup with no vacuum advance.

However, if I'm understanding correctly how vacuum retard works, I think the canister should be connected to a ported vacuum on the TB. And a ported vacuum source is one that is above the closed throttle plate, so that timing is not advanced at idle (no vacuum above the plate) but advanced at part throttle (source is now below the slightly open plate, creating vacuum).

The problem with this model is that the only vacuum port on the TB is clearly below the closed throttle plate. This would be a manifold vacuum source, usually used for advance only, as the advance would be highest at idle (most vacuum) and less and less as the throttle is opened further. There is no "ported" source. Anybody know if this really is a "retard only" system and, if so, how it's supposed to work? I probably need to know that before I test it (IMG:style_emoticons/default/smile.gif)

[r_towle]

Well, my choice is always hook up the vacuum advance and never hook up the retard.

Testing, as you asked in your post, would be simple enough with a timing light while you move the vacuum line from one side to the other of th canister to show you what is up.

There are several throttle bodies with both one and two ports.
There are several canisters with one or two ports.
Makes it hard to know which one you left the factory with.

Rich

[JPA914]

Well, my choice is always hook up the vacuum advance and never hook up the retard.

Testing, as you asked in your post, would be simple enough with a timing light while you move the vacuum line from one side to the other of th canister to show you what is up.

There are several throttle bodies with both one and two ports.
There are several canisters with one or two ports.
Makes it hard to know which one you left the factory with.

Rich

The lines are different sizes, so no chance of mixing them up. I guess I could rig up something for the test you describe, but first I'd like to see if my canister even holds vacuum. Any idea how best to do this?

BTW, I tend to agree that vacuum advance is preferred in general, as vacuum retard was (according to some) a band aid solution ushered in by the first wave of pollution controls. At the same time, though, I'd want to proceed with caution when second-guessing the engineers. Probably could be done, but it might require a different static timing. Not being an expert, I'd be nervous trying that (IMG:style_emoticons/default/smile.gif)