The front 2 screws get turned to tight, a little lite file work,mostly by those screw holes and the the gasket area will clean right up.

Hidden vacuum leak, at the bottom of power step-up piston. Should be gasket at bottom to prevent leaks at idle. Piston should move freely,not stuck in up position. Piston down at idle against gasket.If gasket bad or gone, worse than vacuum leak, will draw air and gas fumes from carb bowl down into intake manifold.