780 vacuum secondaries - Team Camaro Tech
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post #1 of 4 (permalink) Old Jul 13th, 03, 05:28 PM Thread Starter
Senior Tech
Join Date: Dec 2002
Location: Stanley ,N.C.,U.S.
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I just put the original 780 4053 carb with vacuum secondaries back on my 396/375 engine. When the engine is idling and I open the throttle wide open, the secondaries never seem to open. Whats up? Kevin
68SS 396/375 L-78

68SS 396/375 L-78 Camaro
68 Chevelle
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post #2 of 4 (permalink) Old Jul 13th, 03, 05:40 PM
Senior Tech
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Location: LR AR
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They aren't supposed to open like that. Perfectly normal. You need to be putting a load on it while driving for it to open. That is the beauty of vacuum secondaries. They know when to open only when needed. [img]smile.gif[/img]

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post #3 of 4 (permalink) Old Jul 13th, 03, 08:01 PM
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Yup yup. Thats the way it goes. It wont deliver unless it needs to deliver.
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post #4 of 4 (permalink) Old Jul 14th, 03, 02:37 AM
DOUG G's Avatar
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Quick trick to see if they open and how much is to use a twistie in the rod for the diaphram tighten only enough to hold it, not to stop it. Make a run down the street and see if it moved. Only opens under load.

68 Camaro~LSx ~all motor
1.54 60'--6.95 @ 98.45 660'--10.96 @ 121.53
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