The weber 32/36 needle and seat assembly is a delicately designed valve which controls and regulates the level of fuel which is held in the fuel bowl.
How does a needle and seat work? In simple terms, fuel is delivered via the fuel pump through a fuel hose which then enters the carb housing until it greets the needle and seat assembly. This fuel is allowed to enter if the leverage on the float assembly opens the needle off the seat. Fuel will freely flow through the needle valve into the bowl and once this level has risen, the float itself will push upward and close the needle. This process repeats over and over while the engine is in operation and self regulates in various fuel demand scenarios.
These Weber 32 36 needle and seat assemblies are sold each.