Those heat plates or spacer only use one gasket on the bottom, the carburetor sets right on it. Rotate it, flip it, what ever it takes for the slots and hole to align, or as you have done, make a new hole. They never will run right with the alignment right. And while you are checking, make sure the spacer is flat.
I'm betting the vacuum passage to power valve is blocked, not getting manifold vacuum keeping power circuit open all the time.
