The power piston is brass in a bore of alloy. It must be free in the bore. The idle port is below the throttle plate. You have stated that the engine runs good at idle. If the power piston is stuck on the power valve ball a rich fuel mixture is entering just off of idle. When you torque down the power piston assembly, make sure the piston is not in a bind. The manual image will put you in the right pew 'where the power piston is'. Good luck.
http://chevy.oldcarmanualproject.com/Rochester/BBC03.htm
Last edited by Cuthbert; 03/10/2012 4:20 PM. Reason: http correction
