The vacuum advance should only be hooked to a ported vacuum source (no vacuum at idle), not manifold vacuum (vacuum at idle).
There should be no vacuum present at idle but when you start to open up the butterflies then ported vacuum will become present.
The vacuum advance works in conjunction with the centrifical advance and the total of these is added to your initial, this is your total timing.
For instance I.E. 10 initial, plus 18 centrifical, plus 10 vacuum advance will net you a total timing of 38 degrees, which is about where you want to be.
The may not be your problem but its something that needs to be addressed so you can get the most performance out of your engine.
After getting the timing squared away adn the engine off run all your idle mixture screws in till they bottom out then unscrew them all 3 full turns, this is just a starting point. You will probably end up somewhere between 2 1/2 to 1/ 1/2 turns out.
Sometimes you have to drill some air bleed holes in the primary butterflies, a very small drill bit will work, usually less than a 1/8 bit will do the trick, start small and work your way up no sense in getting crazy here, causes theres no backing up once you go to big.
Drilling the holes will add extra air necessary to get carb to idle correctly when using a high lift cam.
Goodluck, Cp