Can tou spray carb cleaner or starting fluid at the point the intake mates to the heads and see if it idles faster revealing a vaccuum leak without harming your engine paint? Sounds like a bad vac leak to me too. My intake is at the machine shop right now after deck bieng cut .018 and new heads being milled .020 (if I remember right) the lower part of the intake at the ports didn't even touch the gaskets, I used a brush to paint the intake (orange same color as engine)where it mates against the gasket then quikley bolted it to the heads to check port match, thats when I found the problem, it only left paint on the upper portion of the gaskets. If not it also sounds like when I used to wash the engine bay of a car I used to own, not saying yours is wet but maybe a cracked rotary button or cap crossfiring under a load. Sorry to here your having so much trouble getting it going though, I hate when that happens. Good luck and hope you find it soon.