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Acceleration Junkie
Join Date: Aug 2007
Location: Laguna Beach, CA
Posts: 263
Originally Posted by rsrmike View Post
. . . I still don't understand why the vacuum appears to retard the trigger?? Did they ever have vacuum retard?
The term, "vacuum advance" is a misnomer. To be gramatically and descriptively correct, the device should be referred to as a "vacuum retard."
Engine manifold vacuum acting on a gasoline engine distributor's "vacuum pot" does indeed retard timing. Distributor timing is advanced by loss of vacuum on the vacuum port.
Easy to observe/verify action of the vac pot using a timing light. At idle, check timing, crimp the vac line, pull it off the vac pot and timing will advance aprox. 18-deg.
Old 11-20-2008, 05:57 PM
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