Trying to use manifold vacuum on Edelbrock Carb?

[AllGoNoShow]

So my Edelbrock 600cfm carb has two 3/16 ports on the front for vacuum and my understanding is that one is for ported (above throttle blades) vacuum and the other (lower port on the right) is for manifold vacuum (per the instructions).

I am trying to utilize the manifold vacuum port, but each one of these ports are acting as ported vacuum and I’m not seeing any vacuum advance at idle?! Just wondering if anyone has seen this before? There is some type of carb adapter between the carb and manifold, is it possible that this is interfering with something? It’s not like it’s plugged, if I put a vacuum gauge on it, both ports will show vacuum when you open the throttle, just nothing at idle.

Nick

[geezer#99]

That adaptor is Likely a heat spacer.
Could be they used a gasket that just happens to cover the port on the base of the carb.
You’ll need to pull the carb off to see.

Or you got a flawed base.

[sweetk30]

brand new edelbrock in my hands for these pics . i hooked up a hose to each port and blew threw it to find the matching ports .

arrow points to the area directly above the bore . the SLOT that goes left to right not up and down is the port hole . one is above the throttle blade and one is below .

2 pics 1 of the throttle open and one shut . you can see one gets plugged off .

[AllGoNoShow]

Originally Posted by sweetk30

brand new edelbrock in my hands for these pics . i hooked up a hose to each port and blew threw it to find the matching ports .

arrow points to the area directly above the bore . the SLOT that goes left to right not up and down is the port hole . one is above the throttle blade and one is below .

2 pics 1 of the throttle open and one shut . you can see one gets plugged off .

Thanks for the pictures!! Although I don't see how the manifold vacuum port on mine is getting plugged now-doesn't seem like an adapter or gasket would have any effect on it. I guess I will have to pull carb off and see where I am at.

[geezer#99]

Take some pics when you do.

[sweetk30]

hook a hose to them and suck air via your mouth and listen . easy to do with carb inplace still to verify before removed .

have you checked to see if the hose has a internal plug ? like a mud dobber bug went inside and made his home and plugged it off ?

also check the vac can on the dist to verify movement with the dist cap off to see .

[AllGoNoShow]

Well took the carb off and both holes are pretty much at the same spot- above the throttle blades (picture attached). Guess that answers that question-must be some type of casting error or something- or carb is older so maybe this use to be how they were made (it’s a 1400 series).

[geezer#99]

Ah! No!
Those two round holes are the idle mixture screws holes.
The slotted horizontal ones are above and below the throttle plate.
Left side ported, right side manifold vacuum.
Hard to see the right side though.

[AllGoNoShow]

If you zoom in you can see them both-both horizontal holes are at pretty identical places-and when the throttle blades are closed (I’m holding them open for this picture), they are both above the throttle blades.

[geezer#99]

Close the throttle and take another pic.

[sweetk30]

Originally Posted by geezer#99

Close the throttle and take another pic.

x2 and waiting