On my 750 holley I have a vacuum port for my vacuum advance on passenger side towards the front and one on the front on the bottom toward the base. I get a vacuum reading of 11 on the side one where my vacuum advance is hooked up but when i checked front one I'm at close to 20. Why am I getting Higher vacuum on the front one? 4-speed, no power brakes.

Your front port is direct vacuum from motor. The side one is ported vacuum---it will be lower then the front. You have it set up right...run your vacuum advance from the side port. If you would run it from the front you will have ALL your advance at idle!!

Brian
72 Elky
71 Chevelle