Which part of the carburetor controls the engine speed?

The throttle is the component of the carburetor that primarily controls engine speed. It regulates the amount of air-fuel mixture that enters the engine. When the throttle is opened, more air-fuel mixture flows into the engine, resulting in an increase in power and speed. Conversely, when the throttle is closed, less mixture enters, causing a decrease in speed and power. This control mechanism is crucial for optimizing engine performance, allowing the operator to adjust speed based on the demands of the task at hand.

In contrast, the needle is responsible for controlling fuel flow and mixture at certain operating conditions, while the float regulates the level of fuel in the carburetor bowl to ensure a constant supply of fuel. The choke, on the other hand, is used to enrich the fuel mixture during startup, particularly in cold conditions, but does not directly control speed during normal operation.