Limit total advance???

[Excaliber]

Generally speaking, the vacuum signal is directly related to the cam profile. And generally speaking the higher the vacuum, the better the engine's overall condition.

At any rate, I bet your mechanical advance is frozen, stuck, sticking, needs cleaning. Your not getting nearly enough mechanical advance added to your base of 20. Maybe 8 degrees mechanical? Pfffft, thats nothing... Follow Rick Parkers excellent post, but instead of worrying about how to LIMIT the advance, look for MORE advance down in there where the sun don't shine. Not welding, get the grinder!!

There are a number of ways to limit what seems to be a very fast and high vacuum signal to the dist. It also appears that you have a very aggressive vacuum advance unit, advances a lot and it doesn't take much vacuum to do it!

For now, stay focused on the mechanical side of things. Putting the advance mechanism UNDER the dist plate was not one of Ford's better ideas. The GM and MSD type dist's with the advance mechanism on top is far easier to service, modify and actually "see".