The relationship between mixture screws and idle speed screw needs to be proper. If the mixture screws are in too far, you can make the carb idle on the main metering circuit - though not very nicely. As Cloaked said, start with the idle mixture screws 1 1/2 turns out and get you idle speed set properly.
If the diaphragm on your power valve (and it should be 2.5) is ruptured, it will run full rich and give you black smoke coming out the exhaust. The only true way to test it is to remove it and hold the outer diameter of it while trying to gently twist the pointy end. If it turns freely it is bad. By turning your mixture screws in all the way, the engine can still run if there is a significant base gasket leak.
S5 WHEEL PACKAGE - FREE SHIPPING
TWO WHEELS W/ST205/75R14 KENDA TIRES $299
TANDEM AXLE PACKAGE W/205/75R14 KENDA TIRES $599
TWO 5 LUG WHEELS W/ST205/75R15 LRD KENDA TIRES $349 S5 W/BLACK INLAY
TWO 6 LUG WHEELS W/ST225/75R15 LRD KENDA TIRES $359 S5 W/BLACK INLAY
$99 LED LIGHT PACKAGE - FREE SHIPPING
REBUILDING HOLLEY MARINE CARBURETORS - $225 DELIVERED
Email - email@example.com