Pull the carb, flip it over and check how far open the throttle blades are set at idle. If your exposing the transition slot at idle the idle screws won't have much effect, so you may need to drill the throttle blades. That should fix the idle mixture.
The only way the power valve would effect this condition is if the diaphram is blown and leaking fuel into the power valves vacuum port, so make sure the PV is a known good one. If you have a mighty-vac vacuum tester it should have a large rubber disk attachment that you can test the power valves diaphram.
If the transition is still too rich (low speed driving, not acceleration) you can lean out the idle bleed (bottom hole in the metering block.)