Main operation of Solex 4a1 carburetor
by Patryk Rebisz

If you were to press on the gas pedal, the throttle plates open and the suction (vacuum) of the engine that pulled the fuel mixture though idle opening would disappear. There would be no suction anymore to pull the fuel through the idle passages but the suction force would start pulling fuel through other orifice. If you were to follow path of fuel at this stage, fuel is sucked in from fuel bowl through the main jet (79) at the bottom of the bowl and enters main mixing tube. In there it encounters preatomizer (85) that mixes fuel with air entering through main air correction jet (145). From this point the fuel is emulsified and is discharged into the carb's throat.

Notice that here the fuel path is much simpler than at idle (the main mixing tubes are simply dipped into the bowl - they don't pass any gaskets) so any air leaks are much less obvious or destructive to driving experience.