What's your Timing set to? *strokers*

The reading should change when you hook vacuum up to the dist. Either the line your using off the carb is a ported vacuum source (which doesn't have vacuum until you open the throttle a little) or your vacuum advance is bad.

BTW: What's your total timing set at? With a performance engine like yours you need to have the dist. recurved for less centrifugal timing that comes in quicker and run more initial timing.

And timing issues shouldn't cause any "pops". That sounds like a misfiring cylinder due to a bad plug or wire.