Trying to adjust a carburetor without a vacuum gauge is the way to get it "close" but it will never be dead on. Attach the vacuum gauge to a manifold vacuum port. With the engine fully warm, and in drive with the parking on and wheels blocked, neutral for a manual, adjust idle speed until it is correct. Then adjust each air screw until you reach the highest reading on the vacuum gauge, then out 1/2 a turn leaner. Then readjust the idle speed as needed.