vacuum advance or retard?

["Philip E. Barnes" <peb3@cornell.edu>]

There has been a bunch of traffic about vacuum advance/retard on
distributors lately. One can quickly tell one from the other by sucking on the
vac. line and observing the direction the breaker plate moves. If it moves
to the direction of rotation, it's vac. advance; if it moves counter to
the direction of rotation, it's vac. retard.

Phil Barnes  '71 TR6 (w/vac. retard)  CC61193