The Stovebolt Site Forums The Shop Area Engine Shop Vacuum at carb line running to dizzy?

First question, when running at idle is the vacuum line at the dizzy suppose to be zero? I disconnected the vacuum line at the dizzy and hooked up my vacuum gauge and and at 475 RPM idle it reads zero.

When I reconnect that vacuum line what would be a good reading range as I increase the speed of the engine. I'll probably have to put a "T" connection in the line in order to get a any readings.

I can't seem to find any written ratings in my shop manual for this vacuum line.

I just checked the vacuum at the side of the intake manifold and at idle its reading 18 inches. The other line at the dizzy coming from the carb is reading zero. Once again is that normal? Trying to figure out this power falling off problem.

You're tapped into "ported vacuum", where the throttle disc is below the port at idle. As the throttle opens, the disc sweeps past the hole and vacuum reaches the distributor.

You'll get at least 2 very strong opinions as to which is "correct": ported or full-time. Based on prior posts, those who are sure of themselves and insistent have the least grasp of how it works.

The answer is: use whichever one works.

The engine was designed to run ported vacuum to the distributor, which will only be there at part-throttle cruise. Then it will be somewhere in the 15-18 inch range. As soon as any load goes on the engine the vacuum goes away and the distributor returns to initial + centrifugal advance. No ported vacuum at idle, and slightly less than full manifold vacuum at cruise. Setting the timing to the BB with full vacuum at idle will result in very severely retarded ignition timing and very low power.
Jerry

The old Stovebolts used ported vacuum for the dist.It will only have vacuum at part throttle. You can watch the dist vacuum work on this by watching the dist as you open the throttle. You should see the dist turn at part throttle. Vacuum advance is basically for economy. It will not effect "power falling off".