Hooking distributor advance to intake manifold port.

It is possible that manifold vacuum will advance timing, reduce engine braking at coast down, lopy coast feeling, and result in high idle speed, under light engine loads. Loads such as A/C or alternator draw from running loads will bring down speed, but you may notice instability, if you desire to adjust and maintain correct idle speed.

When working on the carb, manifold port comes from the base, ported source is from slit passage above the throttle plate.