[lukecp]

For a vaccum advance there are 2 ways you can hook it up.

1. With vaccum going to the vaccum advance at idle (manifold vaccum)
2. Without vaccum advance going to the vaccum advance at idle (ported vaccum).

Pull off the vaccum hose when your truck is idling and stick your finger over the hole...if it tries to suck your finger in, you are running it off of manifold vaccum. If there is no vaccum at the port, it is on ported vaccum.

If your truck has a rough idle and the advance cannister is hooked up to the ported vaccum, hooking it up to manifold vaccum will significanlty improve the idle quality. From what i understand, there is no difference in fuel economy or power either way.

Try hooking it up to the manifold vaccum port and i bet it will idle much smoother. I'm guessing you have it hooked up to ported vaccum right now (i'm not familliar with Holley carbs).