318 Running Richer w/ Carb Swap

Also, the power valve, while it can affect operation if it gets blown, is once again not on the idle circuit, so it has no effect on idle mixture at all. You're kind "stuck" with the idle mixture you have with that old of a Holley. You CAN upgrade the primary metering block with one that has adjustable idle fuel bleeds.....but that ain't cheap. For about twice that cost you could have one of the nice little Quick Fuel carburetors that's fully adjustable on the idle circuit and the high speed circuit. You "should" be able to get that carburetor closer to right than it sounds, as it's pretty lean on the primaries, so try to get the timing sorted out first.