I am checking my power valve(s) too. The valves are located in the "jug". You can see part of them if you remove the pipe. The actuating mechanism is located on the right side of the motor (if you are sitting on the bike). You can remove the small plastic housing (has a small rubber boot on the base). Removing the two screws will expose the valve actuating shaft. The light gray colored cover is about 2" by 1 1/2" or so.
You should be able to grab the mechanism and pull it towards you. The action should be smooth with no rough spots. If this works the valves are not stuck. The next step is to start the motor and rev the engine. I believe that the little arm should move once the motor hits 5,500 to 6,000 rpm. I need to do this test on my bike too. If the valve actuating lever does not move, you have an internal problem. The small plastic drive gear inside the right-side engine cover may be damaged.
I suggest you buy a shop manual so you know where all the parts go once you start taking things apart.
Let us know what you find.