I should have been a little more specific. The float level is set
with shimming washers under the float valve seat; they're fiber washers
that come in a couple of thicknesses to get the level right. If the
carb is a bad dripper the float might have a pinhole leak in it and be
partly filled with fuel, making it sit lower and allow the level to
rise enough to drip out of the main nozzle.
The mixture control doesn't change the float or fuel level. It
applies a bit of venturi suction to the bowl, reducing the atmospheric
pressure in the bowl and holding the fuel back. The bowl is vented to
the venturi wall, and another port passes through the mixture control
valve to a dead-air space behind the venturi that has normal
atmospheric pressure. The venturi suction is constantly drawing air
from behind the venturi through the bowl's airspace, and pulling the
mixture to lean closes off the atmospheric pressure supply and lowers
the bowl pressure. At idle or low power settings, there's little or no
venturi suction and the mixture control has no effect.

Dan