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914World.com _ 914World Garage _ Vacuum advance ports...which one to use on (V8) carb?

Posted by: computers4kids Dec 4 2008, 11:54 PM

I have the carb below on my chevy powered 914. The carb has two different types of vacuum ports...I don't understand the difference. Could someone give me a quick education on the differences and which one is better to use.
Much appreciated,
Mark

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Posted by: Dr. Roger Dec 5 2008, 02:11 AM

full time means below the throttle plate

ported means above the plate, or... only get vacuum under part or full throttle.

but then you've got to verify which dizzy you are using. vacuum advance or retard...

Posted by: marks914 Dec 5 2008, 05:29 AM

You want to use ported, that gives you the vacuum advance when you need it, at light-med throttle, then the mechanical kicks in. If you run it on the manifold side, it will be advanced at idle, and then the timing will drop when you open the throttle, the mechanicals will kick in at their preidetermined time, later.
Mark

Posted by: computers4kids Dec 5 2008, 07:57 AM

Thanks...that makes sense. I'm running the GM HEI distributor.