[RobMcQuarie]

Definitley use ported vacuum, you don't want any vacuum advance at idle, only after the throttles are cracked open. Second, check the rotor phasing. I have found re-man Durasparks that had a point distributor vacuum advance unit in them. The arm that connects to the plate is the wrong length, and moves the plate out of phase, causing the engine to need excessive timing. Had it happen just recently with a customer's engine, we just replaced the vacuum diaphram with a performance one off the shelf and timing fell back into place.