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Is there any way to test the vacuum secondaries on a 780 Holley on the bench? The diaphragm is new, but I think they not opening at wide open throttle.....
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Re: Bench testing Holley vacuum
The secondary diaphragm moves in response to venturi vacuum generated by airflow velocity in the primary venturi, not by manifold vacuum. If you remove the diaphragm housing from the main body and apply vacuum (with a MityVac or similar vacuum pump tool) to the hole in the housing that's sealed to the main body with the little cork gasket, you'll see the actuating rod move and you can determine if the diaphragm is working/holding vacuum. -
Re: Bench testing Holley vacuum
hold the primary wide open and work the secondary by hand and you should hear air being pushed out the holes in the venturies. with the unit off of the carb push the rod into the housing and while holding it there put your finger over the vacuum hole and see if the rod stays retracted. if it come out you have a leak somewhereComment
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