[John S Peterson]

You also have to remember that if you don't get any change with mixture screws you may have the idle screw open too far just to get it to idle. When you do that, the throttle blade is open too far causing fuel to be drawn in from the main circuit. Check positioning od the secondary throttle blade and make sure that the blade is just barely uncovering the transfer slot. The adjustment for that is reachable from the underside. If you run to radical of a cam you may need to drill small holes in the blades to get the engine to idle without having to open the throttle blade too far. I have tuned many Holley's and this is the best way I have found to allow an idle mixture adjustment. Remember, the wider open the throttle, the greater the pressure differential, which changes the "signal" the carb circuits respond to. Good luck. Also what everyone else said about power valves is true. Drop to 2.5"s and make sure you are using the right gasket (as they made 2 different ones). That should allow you to get some adjustment