B&M Converter is bad

You will reach a point where you don't gain more. There should be a sort of "flat" spot on "top" of the maximum vacuum reading, where it does not increase. "Just touch" the screws CW (lean) until you JUST DETECT either an RPM or vacuum drop. In other words you want the pretty much "peaked" but on the "lean side" of the peak.

You want the last adjustments made with the idle close to where you want it speedwise.