If you run the engine up and try to find the maximum centrifugal advance, what does it turn out to be? And at how many rev's?
Do you have a special curve in the distributor - or is it simply advanced out on the low end to get it at the right spot when you are at cruising rpm?
Otherwise I'm thinking like John - vacuum can doesn't fully retract its operating rod at engine stop.
Steve Metzger Tucson, Arizona