Carburation

The principle of carburation.

The function of a carburettor is to mix air and fuel in the correct ratio of 15:1, by weight, to create a combustible mixture for an internal combustion engine. It does this by using the Venturi effect to draw fuel into the airflow.

In a carburettor, air is drawn into the engine through an air intake and passes through a narrow passage called a venturi.

As the air flows through the venturi:

• its velocity increases, and
• its pressure decreases.

This causes fuel to be drawn from a fuel bowl into the airflow and mixed with the air in the venturi.

The fuel-air mixture is then delivered to the engine through an intake manifold.

The carburettor uses various components to control the amount of air and fuel that enters the engine.

The throttle controls the amount of air that enters the carburettor, while the fuel bowl and float control the amount of fuel that is delivered to the venturi.

At full throttle, the carburettor does supply the engine with a richer mixture. This richer mixture contains a higher proportion of fuel relative to air. The reason for this is to provide extra fuel for cooling the engine. When the engine is working at full throttle, it generates a lot of heat.