Be sure the piston rod isn’t bent. It needs to press straight down on the power valve.
Be careful when removing the power piston. The stem can break off easily. Push down on the stem and spring with your finger, then let it snap back. Do this over and over until the piston comes out. A frozen stem is another problem all together. Try spraying silicon spray lubricant into the vent hole.
The power piston presses down on the pin sticking out at the top, allowing extra gas to flow.
The power valve sits on the bottom of the 2 Jet carburetor, between the 2 main jets.
The illustration on the left is for the early 2 Jet carburetors. Part #56-2. 5/16″ threaded end.
This does not work on the marine 2 jet carburetor.
There are 3 other power valves to consider.