Are you getting the required 0-1 mm clearance on the control choke arm? If not, loosen the lock nuts on the throttle cable and adjust.
Next, move the throttle to CHOKE; does the choke fully close? If not, turn screw B OUT until the choke closes, then turn it a small bit IN until it contacts the control lever.
FYI screw A is used to set the maximum speed (FAST) to 3,100 +/-50 RPM.