I've never rebuilt that particular Holley... but Holley's in general are very particular about the float height setting. Again, I lack familiarity with that carb... but your issue sounds like the idle jet is set too rich. If that's not sealed, tighten it in a bit until it stumbles and then back it out a bit. What I remember most about the double pumpers on the windsors we had... if the float was too high or the needle stuck open they would simply overflow the well and run it down the throat, thus the rich condition you presently have. I know this one is updraft and a bit different principle... but possibly the same problem. CHECK the float and needle.