Test your power valve by taking it out of the carb and placing a quality hand vacuum pump to the diaphragm side.
Squeeze the pump until the diaphragm pulls in. Look at the dial reading at that point. YOU will need to use the cup that comes with the pump.
If you use a good pump ( one that has a bit of accuracy ), you should be able to get an idea of when YOUR valve begins to work.
Hope this helps.
