[Cobra 29]

I have a 351W SVO crate motor with the FMS ignition system made by MSD. The distributor is a Duraspark with a vacuum advance module. The vacuum advance is not working. I thought it was because of a broken advance module. Wanting the ability to limit (adjust) the vacuum advance I ordered and installed the adjustable Crane Cam vacuum advance module. It too did not advance the timing. The vaccum port on the carb is working per my vacuum gauge. The signal is timed for part trottle (no vacuum at idle). Inspecting the top plate in the distributor, I found that it will rotate clockwise toward the vacuum advance module but it takes a lot of force. After manually rotating (clockwise to advance) the top plate it will rotate counter clockwise back into the original position. It seems to have strong springs. I believe these springs are too strong for either vacuum module. What could be wrong with the distributor? I know it is not a MSD! Thanks in advance !!!