How much vacuum do you get at the distributor at a steady 1500-2000 RPM? If it's over 15 inches, you should be getting full advance, but only at a steady cruise RPM. Snapping the throttle won't allow the distributor to move, or you might just get a little movement.

If you're running dual carbs, it might be necessary to Siamese both ported vacuum lines together to get enough vacuum to keep the advance in full CCW for cruise.
Jerry

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