Quick fuel carb fuel pressure too high? Rich idle...

Ok Guys. Here's the video Mark Whitener made opening an externally controlled power valve while the engine is idling.


Here's the technical explanation why, in most cases, the power valve (or step up) has no appreciable effect on idle mixture.
Motorsports Village • View topic - Power valve flow ????

Are there exceptions? Yes. When the idle jet and/or PVCR is large relative to the normal relationship with the main jets. These are situations when opening the power valve (or raising the rods) can cause a significant change in the pressure in the main well which in turn causes an increase in flow into the idle well.
See Shrinker's post 7 & 10 in the archived thread here:
Power Valve Question