Did your old carb have both of those screws ?
So you have bought a junk carb off Scamazon and this is not the carb the engine came with .
The High speed ( throttle open ) is determined by the main jet at the bottom of the transfer tube
In the side there should only be one screw , the long one with the spline on it which is the idle mixture screw and sets the air:fuel ratio
The screw behind the welch plug is the idle volume screw which controls the volume of the air-fuel mix entering the cylinder when the throttle is closed on the throttle stop
I have not seen one of these for decades .
Usually it is done with a series of small holes
And your picture is way too small to be of much use .