[rich weyand]

You don't need to plug the vacuum line on the carb, but you can if you want. I never bother. You can pull all the plugs out and spin the motor with the starter to measure timing, as long as you have the #1 plug wired and grounded. It is a purely mechanical setting.

Yeah, if you were going to drive it around like that, you need to plug it. But not just to measure timing.

The reason your idle timing is the same as your timing with the can disconnected is that you are connecting to ported vacuum. That's part of your problem. Connect the vacuum to the manifold vacuum port. Then set base timing, with the vacuum advance can disconnected, to 12* BTDC.