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Pontiac Forum: Hei ported or manifold vacuum
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  #1  
Old April 22nd, 2018, 09:57 PM
Lemansddj Lemansddj is offline
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Hei ported or manifold vacuum

Ok I got a 1970 Pontiac 350 with a summit 600 cfm carb and was wondering if the vacuum advance should go on ported or manifold ports
I heard that manifold vacuum could help keep the temps down while in traffic
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Old April 23rd, 2018, 09:23 AM
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melsg5 melsg5 is offline
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You are correct running the line to a constant vacuum source is preferable to a ported source. The ported source came about due to emissions restrictions. Prior to that there was no ported source.
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Old April 23rd, 2018, 09:36 AM
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cammerjeff cammerjeff is offline
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While I agree with melsg5 that manifold vacuum is usually best for vacuum advance, I have seen some individual cars that ran better with ported vacuum source. I think it has a lot to do with the specific cam shaft, and how worn all the componates are.

But I always start out with direct manifold vacuum on the Dist.
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Old April 23rd, 2018, 03:19 PM
Lemansddj Lemansddj is offline
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thanks
I have it on manifold now and will adjust the curb idle speed and the air/fuel mixture screws

maybe this will help with the off green light bog
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Old April 26th, 2018, 07:14 PM
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avell007 avell007 is offline
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Check your carb accelerator pump for that off idle bog , if you think it's timing you could put lighter springs on the centrifugal advance so it advances quicker off idle .
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Old April 27th, 2018, 11:50 AM
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how did you mount a Summit 600 cfm carburetor on a Pontiac manifold, factory Pontiac is spread bore the carburetor is square bore. Which intake manifold are you using?
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Old May 1st, 2018, 01:43 PM
Lemansddj Lemansddj is offline
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Sorry I did not it is on a Edelbrock performer intake
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Old May 1st, 2018, 02:38 PM
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the carburetor looks a lot like a Holley. With the engine off disconnect the throttle return spring. Hold the throttle wide open and at the same time press down on the primary accelerator pump arm. You should be able to insert a .015 feeler gauge between the arm and the adjustment screw on the throttle linkage which presses down on the arm. The video below explains the adjustment.
https://www.youtube.com/watch?v=k-Nx5HEzvlY
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