I'm confused on timing my new rebuilt 312.  Trying to time it by the vacuum method along with a timing light. As I advance the distributor to increase vacuum reading it does run much better but the vacuum advance can hits the intake manifold when I reach 17" hg @20 degrees advance. I'm sure I could get a higher vacuum reading yet if I pull the distributor and rotate it a notch but I'm concerned about the initial advance climbing over 20 degrees. The engine does have an Isky E4 cam advanced 2 degrees, the Mr. Gasket lighter advance springs along with a rebuilt distributor modified per a post here to give 26 degrees centrifugal advance. Is it possible the springs are too light allowing extra advance @ idle or?    Dave v

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