Well you got it right, the slot in the gasket is how the manifold vacuum is ported to the hole in the base of the carb. If it doesn’t line up then I would say you’ve got the wrong gasket. Just file or cut the slot over to line up with the hole in the base or better yet, get the correct gasket.
It sounds to me more like you’ve got a bad accelerator pump. Look down the throat of the carb and make sure that your squirting fuel into the venturi when you operate the carb.
Sticking power valve would usually show up with a loss of power when the engine is under load. When the butterfly is open under acceleration or load and the vacuum has dropped to nil the spring under the power valve pushes it up and moves the ball check off the jet in the main well and adds more fuel all during this period of operation. The power valve has very close tolerances and any dirt/sludge/gum/scratches or burrs can cause it to stick, it’s not unusual to find the stem bent also after they have been worked on. The correct spring pressure is critical to its proper operation. If the carb has been worked on, the gasket under the main well is often the wrong one or installed incorrectly causing the main well to sit on the air horn cocked, then the stem on the power valve doesn’t line up properly.
And finally, as the carb king would tell ya, the problem might just be that, it’s a Rochester!!!
Denny Graham
Sandwich, IL

Denny G
Sandwich, IL