Wich one is ported vacuum and which one is Manifold vacuum on my "71" 455 carb?

Trying to get my distbutor set just right, following the "power Timing" thread that Larry70GS put up and recomended when getting vacuum for your vacuum advance , he recomended using manifold vacuum.

In this picture you see 3 vacuum lines going to my carb, 2 are plugged off, the 1 is going to my vacuum advance on my distributor, is it hook to the right vacuum port? Im looking for the manifold vacuum one. I Dont want to hoook it into ported.




Thanks

 

I do believe the port you have the hose running to the vacuum advance on your distributor is ported. The smaller port on the far left (passenger side) of the carburetor may be full manifold vacuum. The way to tell is, with the engine idling (be sure the choke is fully open and that the fast idle cam and screw are not engaged), pull the bolt plug out or the hose off the port and see if there is vacuum present. If the port is full manifold vacuum, there will be vacuum there all the time, especially at idle. If it is ported, no vacuum will be present at idle until the throttle is opened a bit to expose the port to vacuum.:Smarty: Hope this helps.

 

Chris, 1) to be direct in response to your question, I don't know. I'm sure someone on here does know and will help. 2) You should know that your distributor advance mechanism determines which one you must use. Ported vacuum is zero at hot idle and rises in response to throttle butterfly opening to a maximum value and decreases with increased opening and thereby reduced intake manifold vacuum. So, it advances the spark first at tip in throttle and then lets it retard back to base under heavy load. Increased rpm lets the mechanical advance determine maximum wot timing. 3) With engine at temperature idling, remove each cap one at a time and check for vacuum. If you find no or very low vacuum, see if it increases as you crack the throttle, if it then returns to near zero at WOT, it is ported. If it shows full manifold vacuum and follows the curve the same, it is mfld vacuum. Use a guage for your checks. Once again, your distributor determines which to use. TexasJohn P.S.

 

The picture is showing the distributor connected to PORTED vac.
The larger port on the right (passenger) side is full manifold vac.
You will have to force the hose over this one. It is larger.

Hope this helps.

Take Care

 

My answer as well. The plugged line is on the manifold vacuum.