For what it is worth, the March 2014 issue of Hot Rod magazine details a procedure to check for an incorrect fit of the manifold to the heads. It starts on page 124 and is quite educational even though the engine in question is a big bock chevy. It is well worth the read.They used lead shotgun pellets(.110-.112 dia.) and drilled .200" holes in a spare set of intake gaskets, then bolted on the intake without end seals. After torquing they removed the manifold and miked the pellets to see how much was needed to machine the manifold to seal it. I suspect that your motor has a manifold sealing issue.[/QUOTE
Good tip.