The carb solenoid rams a rubber plug up the main jet to cut off the fuel supply so in those last 10 revolutions of the engine fuel will not get drawn into the engine and pass through unburned.
Apparently this massive amount of pollution will kill all life forms with 20 miles of the mower :laughing:
It is energised from the ignition switch.
If there is 1 wire then that should be 12V + when the ignition is on and 0 V when the ignition is off.
If there are 2 wires, the black one is ground.
Without power the spring jambs the plunger int the main jet and the voltage holds it open against the spring so it gets quite hot in use.
Being at the bottom of the float bowl any water that accumulates in the float bowl will cause it to rust and fuel evaporating will lea gum on its rod both of which will wreck it and they cost more to replace than a full seasons worth of fuel.