What about looking at this the other way... at idle the vacuum advance is all-in (to give a cleaner idle with a big cam), which is too much for the engine under load at low rpm. So couldn't you also say that it's reducing the advance to the proper amount when you touch the throttle?

good stuff here.... i know the edelbrock carb needs work too. i know holley stuff not the edelweber carbs. This weekend Im gonna pull the valve covers to see whats under there. Was driving the car a little to get a feel for the motor. Feels real soft compared to a build I did some years back. I think some serious tuning days are in order.