What is the primary function of a diffuser in a carburettor?

The primary function of a diffuser in a carburettor is to control the mixture strength over part of the engine speed range. The diffuser works by creating a venturi effect, which is a reduction in pressure as the air flows through a constricted section of the carburettor. As the engine draws air through the carburettor, the reduced pressure in the diffuser draws fuel from the float chamber into the airstream, mixing fuel and air. This process is crucial for maintaining the correct air-fuel mixture, especially under varying engine speeds and loads, which ensures efficient combustion and optimal engine performance.

The other options, while related to the functioning of a carburettor, do not accurately describe the primary role of the diffuser. For instance, venting air from the float chamber is not a function of the diffuser; this is more about the fuel delivery system. Emulsifying fuel during engine acceleration pertains to the mixing of fuel and air under specific conditions but does not define the main role of the diffuser itself. Finally, adjusting the engine slow running speed pertains to the idle adjustment systems, which are separate from the diffuser's function.

Thus, understanding the diffuser's role in controlling mixture strength helps clarify its importance in the overall