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Old 08-06-2006, 05:07 PM
72Orange 72Orange is offline
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Ported Vacuum

My engine builder set my dizzy up to run no vacuum advance. I'm having some driveability problems, hesitations and bogs that I've been blaming on the carb, but I know that vacuum advance will help my idle quality and driveability so I want to set it up.

I have a 4150 Holley 750 DP, model 4779-3. And there is no manifold vacuum port on the carb. I thought it was the vacuum port just to the left of the front bowl sight level plug, but that port has no vacuum at idle. The other two vacuum sources are the PCV port on the back of the car, and another vacuum source on the front of the carb towards the passenger side that ALWAYS has vacuum.

Reading Holley's manual I see this:

"TIMED SPARK PORT - CONNECT DISTRIBUTOR ADVANCE HERE Note: There might not be any vacuum here at curb idle".

And then it says:

"The timed spark fitting does not provide vacuum for distributor advance at idle. Vacuum advance is available as soon as the throttle is opened from idle and the engine is placed under load, such as acceleration or cruise."

So question is ... where do I get manifold vacuum from on this carb? Has anyone else run into this problem?

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