The Stovebolt Site Forums The Shop Area Engine Shop ported vs manifold vacuum

I am still trying to work the bugs out of my 52 Chevy car. I noticed that at speed, the timing seemed way off until it dies. The car idles great, drives well for the first couple of miles, and then runs out of steam. When I checked to see if the vacuum advance, I noticed that it only worked when hooked up to the manifold vacuum port. When hooked to the base of the carburator, it did not work at all. I've disassembled the carb and verified that the port was free of any blockage.

I also tried to swap carbs from a couple of other running/ driving vehicles. Unfortunately, my car has a 216 with a Rochester carb, all of the others had 235s with Rochester carbs. The mounting base is slightly different between the 2 engines. I

Any ideas why the vacuum advance would work at one point but not the other?

Kael

i believe your car is supposed to run on manifold vacuum ,but should check a manual

Lets fix the important things first. "Running out of steam" is not caused by the vacuum advance. It is mostly a MPG booster. It has little to do with the driveability. You probably have a fuel system problem or possibly the valves are adjusted too tight.
Ported vacuum only works at part throttle. Accelerate the engine & see if there is vacuum at the outlet fitting on the carb. If not the fitting might be plugged or a gasket may not have a passage for it. All these old sixes around that era ran with ported vacuum but you can experiment. If it runs better with manifold vacuum you can run it that way.

yeah that's right i checked with the manual (the ole man )they are ported vacuum .you have to open the throttle to break the throttle plate's open to get vacuum to the advance .