John, you mentioned you changed the intake gasket already and that should "rule out" vacuum leaks. maybe there's a hairline crack on one of the ram tubes which opens up slightly or perhaps one of the castings beneath the carb is porous? How about running it on a single 4bbl? Maybe break out the can of quick start and start ( if you havent already ) looking for an external leak someplace. Worst comes to worse just dont make any left turns :) Mike