No WCFB vacuum at idle

[Troy P.]

Following directions I found on line to adjust idle mixture on my 4 bbl 1955 WCFB I connected a vacuum gauge to the vacuum port on the carb. Rather than the desired vacuum at idle this resulted in a reading of no vacuum at idle. Vacuum jumped up when engine was accelerated.

Mixture instructions say to adjust to get max vacuum at idle and no stumble. Can't do that since I have no vacuum.

Any solution to zero vacuum or other method to adjust idle mixture?

[Edward J.]

Re: No WCFB vacuum at idle

Troy, your likely hooked to a ported vacuum port which will not show vacuum at idle, is there another source that you can hook up to?

[Troy P.]

Re: No WCFB vacuum at idle

This port is at the baseplate of the carb. And directions said to connect there. So I did. But, like you, I was thinking this was a ported vs. non-ported vacuum issue. I don't see any alternative place to connect.

There is a square plug in the manifold that may or may not be removable after all these years. If I could get that out and put a brass fitting in its place would that make a difference?

[Gene M.]

Re: No WCFB vacuum at idle

Troy I suggest the port is plugged some how. A WCFB carb has small bores and should have tons of vacuum at the base to manifold.

[Troy P.]

Re: No WCFB vacuum at idle

It does show vacuum when I accelerate. Think that might still indicate a plugged situation?

If it pulled too much vacuum at idle wouldn't it activate the vacuum advance too early? I don't know what the specs are on my Delco 085 VAC. My vacuum gauge instructions indicate around 20" is normal at idle

[Duke W.]

Re: No WCFB vacuum at idle

Test the VAC start/stop points with a vacuum pump. I don't know the085 specs either, but it's probably something like start at 8", stop at 15" with about 15-16 degrees max added advance. Specs should be in ST-12, AMA specs, or an old Motors Manual, but I don't know if the 085 is OE for your engine.

Manifold vacuum must be associated with the idle speed you measure it at. 20" seems a bit high. I would expect about 18-19" @ 500 idling in neutral with a manual trans. If PG measure in Drive @ 450-500.

Duke

[Troy P.]

Re: No WCFB vacuum at idle

The 085 is the original VAC but I have had it rebuilt. It was leaking. Possibly new specs now?

You are correct that at my altitude, 2500 feet, I should read about 18 at idle.

Do you think the carb baseplate will give the vacuum I would like to see? Or do I need another location?

[Duke W.]

Re: No WCFB vacuum at idle

Check the start and stop points and compare the "Hg to the specs in ST-12 or the AMA specs that you can download from the GM Heritage Website.

I'm not that familiar with the WCFB, but I believe all were set up for full time vacuum advance, other than those engines that had the no-VAC dual point distributor.

Someone who is more familiar with the WCFB than me needs to chime in on the proper location and functioning of the VAC port.

Duke