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  #1 (permalink)  
Old 04-17-2019, 05:25 AM
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Default Secondary Diaphragm Question

I have a 427 side oiler with two 650 Holley 4 barrels. I'm thinking I might have a vacuum leak but not sure. There is a small rubber hose (aprox 3/16 ID) that goes from the front carb diaphragm to the rear one on the left side of the carbs. If I pull one end off and apply a vacuum coarse I get nothing, no vacuum will accumulate. Should it hold a vacuum or is it open to atmosphere? I'm getting all kinds of theories but I want to be sure.
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Old 04-17-2019, 06:39 AM
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That is to balance the opening of both carbs seconaries at same time
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Old 04-17-2019, 04:03 PM
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Where those diaphragm housings bolt to the carburetor body there is a small cork o-ring gasket that seals the vacuum passage from the carb. It's something than can go bad or may have got lost or misplaced when someone had them apart. That would prevent building vacuum although if you can't get either carb diaphragm to hold vacuum with a pump - it would be a bit unusual to be missing the gasket on both of them. If this is your issue you aren't getting secondary throttle either.
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Old 04-17-2019, 05:54 PM
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Quote:
Originally Posted by classical glass View Post
I have a 427 side oiler with two 650 Holley 4 barrels. I'm thinking I might have a vacuum leak but not sure. There is a small rubber hose (aprox 3/16 ID) that goes from the front carb diaphragm to the rear one on the left side of the carbs. If I pull one end off and apply a vacuum coarse I get nothing, no vacuum will accumulate. Should it hold a vacuum or is it open to atmosphere? I'm getting all kinds of theories but I want to be sure.
Thanks.
That hose is fitted to balance the two diaphragms, so the two secondaries open by the same amount at the same time.

Between the two housings, there is venturi vacuum in that hose, not manifold vacuum.

What symptoms do you have, if you believe you have a vacuum leak?

Gary
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