Duck,
Brandon about covered it. This fuel level regulating mechanism is known by highly trained professionals as the "toilet tank" mechanism. If you want to know how it works, take the top off the tank behind the toilet, flush and observe. : )
Seriously, you do need a way to turn off the gas because needle valves do leak and your carb will flood while the ped is parked. You can carry a pair of vise grips and pinch the fuel line (not recommended), or pick up an in-line shut off at the lawn mower or hardware store (recommended).
You do not need this to start the ped. You do need to follow Brandon's advice and clean the carb.
Pedal away.
Ron