What does the Venturi in the carburettor choke tube create?

The Venturi in the carburettor choke tube plays a crucial role in fuel atomization within the engine's intake system. As air flows through the Venturi, the narrowing of the tube creates an increase in the velocity of the air while simultaneously causing a decrease in pressure. This drop in pressure generates a depression over the fuel discharge nozzle.

The significance of this depression is that it helps to draw fuel from the carburettor's float bowl into the airflow, allowing the fuel to mix with the incoming air in the correct ratio for combustion. This process is essential for the efficient operation of the engine, ensuring that it receives the right amount of fuel for the air it is ingesting.