Here's a few basic things to know:
Mechanical Advance - A.K.A. Centrifugal Advance. Uses springs and counterweights to advance the timing with engine RPM's. Kits are available to re-curve the advance. In other words, change the way the timing is advanced with the RPM's.
Vacuum Advance - Uses a vacuum diaphragm to move the triggering device (points or electronic pickup). This advance is a little more accurate than the mechanical, and helps you out with fuel economy.
Most stock Ford distributors are dual advance, meaning they implement both types. You'll also run into single and dual point distributors. One uses one set of breaker points, the other two sets - don't worry about that much other than knowing which type you have.
Hope some of this helps.
-Brian
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Updated: 4/13/2001</font color=red>
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