Advance question

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I've been trying to get my old 307 tuned and optimized as much as I can lately and I ran into something that is a little confusing.

I've got an old Mallory dual point distributor that I converted to electronic, so that's all good, but the advance has me a little puzzled. Mallory says the vacuum advance should start to come in at about 7". At idle (about 850 rpm) I've got 15-16". If I disconnect the vacuum line to the advance canister, the timing mark doesn't move.
Do I have a bad vacuum advance unit or do I need a different one for lower vacuum?

Also, at 850 rpm it appears that the mechanical advance is already coming in. Do I want to get a curve kit and put in some stiffer springs to move it up a bit?

Tim