Help on tuning 408 that's running rich

one thing that i can think of is the power valves. if the power valves are 4 slotted-hole ones, they are high-flow units. you could try a std flow one with the same ``vaccuum level``. that means if what you have is a 4.5 hi-flo (125-145 holley) , you could try a 4.5 std flow (125-45) which will have only 2 slots on its side. for what they cost, it is definitely worth trying. it will get your mixture leaner. most carb kits come with hi-flo power valves wich isnt always a good thing.