What can be used to alter the "mixture" or ratio of petrol to air?

The air screw is an important component in the carburetor system of an engine that directly influences the mixture of petrol (fuel) and air entering the combustion chamber. By adjusting the air screw, you can change the amount of air that mixes with the fuel, effectively altering the air-fuel ratio. This adjustment is crucial for optimizing engine performance, fuel efficiency, and emissions.

When the air screw is turned, it either allows more air into the mixture, enriching the fuel-air ratio or restricts air flow, leaning the mixture. This fine-tuning capability is essential for achieving the correct combustion process, ensuring that the engine runs smoothly and efficiently across different operating conditions.

The throttle body is primarily responsible for controlling the amount of air-fuel mixture that enters the engine but does not adjust the ratio itself. The fuel pump delivers fuel to the engine but does not have an impact on the air-fuel ratio directly. The vacuum hose is involved in conveying pressure changes within the engine but does not play a direct role in altering the mixture ratio of petrol to air.