While holding the throttle wide open, turn screw in (clockwise) about 1/6 turn to reduce RPM about 200 RPM. And of course, turn screw out to increase RPM. Stop screw has a nylon patch to keep it where it is set.
Then go through the process again until the desired RPM is reached.
You will not only have the best mixture at that RPM, but it can be readjusted if major conditions change or carb is installed on a different motor.
Take time to do this right! Proper adjustment is critical to sharp throttle response.
Sketch B shows butterflies set too low. This will result in
poor idle or (most likely) no idle. There is only one correct position of
front butterflies as shown in Sketch A. NO EXCEPTIONS. More or less idle air is delivered by adjusting REAR butterflies.
Sketch C shows primary butterflies set too high. This is
usually done to try to get desired idle RPM. This will result in a stumble off idle.