I would disconnect the VacCan for testing. I wonder if you have it hooked to something that reducing timing underload. I would run a bit more timing it in too. Add 2 degree's initial.
What rear gear? That cam isn't real good for off line power anyway. You can work it out though. Unless you are way down to 2:73 or something.
Where is the fuel pressure measured at?
You should get 17-18" of vacuum at idle with that cam.
Last it's common to have the secondary's closed to far at idle and the forces you to open the primary's to get a decent idle and that uncovers the idle transfer slots which makes the needles sluggish to respond or otherwise not at all. The carb then idles partially off the main circuit for which there isn't enough vacuum signal to properly atomize fuel. The fix? Open the sec a little so you can close the primary's and regain control of the idle circuits. BG can give you a decent starting place on settings but the final adjustments are up to you. Do not be afraid to get outside of the normal realm as long it works for you.