[SkinnyG]

The Princess Auto vacuum gauges work fine. They're cheap. Also check Canadian Tire - they often have good pricing, especially sales.

Is your engine stock? Does it idle nice and smooth?

If so, I'd expect to see it pull about 18" of vacuum at idle. If it's way low, or all over the place, you may have other problems. The gauges usually come with diagnostics inside, otherwise Google is your friend.

Try to get the engine idling around 550 in drive (but not driving - have a lackey on the brake pedal), and play with the mixture screws.

Transition ports....

There is a wee hole below the throttle plate that fuel comes out at idle. The size of which you can change with the mixture screws (they are tapered, and fill the hole, making it smaller).

As you open the throttle further, you reduce the engine vacuum being applied to that hole, so more holes (or in this case, a vertical slot) are placed at about throttle plate height, to allow more fuel to enter the air stream.

These slots or ports ~transition~ from the idle circuit (the hole below the throttle plate) to the cruise circuit (uses venturi vacuum - that restriction near the top, way above the throttle plates).

If the idle speed is too high (the throttle plates are open too far), these transition slots are uncovered enough that extra fueling will be provided into the air stream. If the engine is running more off the transition ports than the idle ports, the idle mixture screws will do nothing.

SO....

Find out why it's idling so high, and fix that. Then play with the mixture screws.

And yeah - set your ignition timing so that you are about 36° full advance with the vacuum advance can disconnected. Princess auto has a cheap advance timing light that works fine and is surprisingly accurate.

Theoretically your base timing will end up being around 10° (might be 8°, might be 15°, it doesn't really matter that much), but you can only check base timing at about 550rpm so that no mechanical (centrifugal) advance is happening.

The fun part....

Base timing, mixture screws, and throttle setting are all related. Mucking with one is affected by the others. You kind of have to much with all of them.

I usually get the idle super low, and set the ignition timing first. Then balance the mixture screw and idle speed screw. More fuel makes it run faster, so you have to reset the idle lower.