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Old 10-11-2012, 10:59 AM
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Carb question about secondary barrel control

Is any advantage to using a secondary that is controlled by a vacuum source vs. air valve?

As I understand it an air valve is a "flap" that is held shut by a spring and when engine vacuum is sufficient to overcome the spring, the air valve will begin to open allowing air to move into the secondaries. More vacuum, more open, more air.
Examples: Q-jet, Edlebrock Performer 1406.

A vacuum controlled carb will use a ported manifold vacuum source to actuate the secondaries. It will have a spring controlled rubber diaphragm.
Example: Holley 4160

It seems to me that the the vacuum pod will be more precise, but more prone to wearing out and failure. Thoughts?
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