Glad you got THAT part figured out, BUT, let's clear something up. The power valve is not on the idle circuit. As the name implies, it's on the...wait for it...power circuit. So, a 6.5 power valve won't open until the vacuum reading gets below 6.5, so it sure AIN'T open at 10hg. Even if it was, it would have ZERO effect on the fuel mixture, because in order for it to do that, there would have to be more air than at idle flowing over the boosters. In short, ifin you wanted to, you could disassemble that carburetor, remove the power valve and throw it in the ditch, reassemble it and start the engine with no effect whatsoever on the idle. Your problem is elsewhere, like idle fuel restrictors, or air bleeds. If you can tell us EXACTLY what carburetor with a part number or list number, we can guide you on how to tune it correctly.