Rochester Guru?

[bkreutz]

I agree, I'm still thinking vacuum too. But after all this time and messing around, I wouldn't rule anything out. Taking the front of the motor apart is a real pain, but there has to be an answer. Maybe have a second set of eyes go through the obvious stuff again.

[Lance]

One thing you might try before getting in the motor is to make a metal plate and install it between the exhaust manifold and the intake. Basiclly isolating the two manifolds. It worked for me.