All this manifold vacuum talk...so, I went and checked mine...wtf?

[Conroe Powdercoating]

51 cranbrook, 218, bone stock

at idle, with vacuum guage connected at the nipple seen on the side of this carb, I get zero vacuum at idle.

when rpm's are increased it goes all the way up to 21 vacuum.

If you look at the carb nipple, you can see by the shape of the body that it leads up and into the throat of the carb.

The other raised channel is the port on the bottom of the carb that leads up to the carb bowl vent.

 

from reading the other thread, I think I am supposed to have 21 vacuum at idle? I dont see how its possible with the nipple running to carb throat instead of getting vacuum source at the manifold somewhere (there isnt a spot as you know)

 

By watching the vacuum guage, I see the distributor advance is getting vacuum when it needs it at rpm's, so I am majorly confused.

Edited July 13, 2014 by Conroe Powdercoating

[Don Coatney]

Two different things. Manifold vacuum, and ported vacuum.

 

Manifold vacuum reads high at idle and goes way down when the throttle opens. Manifold vacuum is where you should connect the vacuum gauge.

 

Ported vacuum goes high when the throttle opens and that is where your vacuum advance line connects.

 

This picture shows the ported vacuum line connected to the base of the carburetor and the manifold vacuum line connected to the SS plate where the original carburetor was mounted. This manifold connection will be different on a stock engine.

 

[james curl]

Look on your intake manifold towards the rear and you should see a boss with a fitting and hose going to the windshield wipers.  This port will provide manifold vacuum for your gauge, probably around 18 inches at idle for an engine in good shape.

[Don Coatney]

Look on your intake manifold towards the rear and you should see a boss with a fitting and hose going to the windshield wipers.  This port will provide manifold vacuum for your gauge, probably around 18 inches at idle for an engine in good shape.

Dodge may have electric wipers.

[Conroe Powdercoating]

my wipers are electric, Ill go look for the vacuum port though.

Don answered, mine does exactly as he said it should, my confusion was the difference between manifold and ported vacuum. I could see how the advance would like what the ported vacuum was doing but didnt see 18-21 at idle and it was because I was reading ported and not manifold vacuum.

[Don Coatney]

Ported vacuum works on the venturi effect.

 

 

 

[Conroe Powdercoating]

I went and looked and yup on the manifold port, so I removed the plug and screwed in a brass nipple and I find that I have 20 at idle, my points are still set at .018