>Vacuum retard is a device designed to provide a smoother idle.
***********************************
Sorry, no flame intended, but. . .I beg to differ. . .The primary reason
that manufacturers started using a vacuum retard unit was for emission
control purposes. If it provides a perceived smoother idle, it did so at
the expense of engine efficiency. *Most* vehicles prior to 1968 used only
a vacuum advance and if anything used a ported line to cut the advance at
idle but not retard it- (Severely) retarding the timing at idle provided
reduce emissions at the expense of engine efficiency. In some cases to
reduce these emission components enough to meet standards, the reduction
was so extreme that the engine would overheat after a prolonged idle, and
as such manufacturers started using temperature sensitive valves in the
coolant lines that would restore the advance (or simply block the retard)
so that the timing would be restored to a more optimum one increasing
efficiency and allowing the engine to cool down.
Barry Schwartz (San Diego) bschwart@pacbell.net
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