Lesson 1/Learning Event 2
FIGURE 9. THROTTLE VALVE ASSEMBLY.
Probably the most important control on the carburetor is a device to change the amount of air-fuel mixture
going to the engine. Without such a control, there would be no way of changing engine speeds. This
controlling device is the throttle valve assembly, which is a round, flat disc mounted on a shaft. The throttle
valve and shaft are near the bottom of the carburetor bore and in the path of airflow. The throttle valve
shaft is connected by linkage to the accelerator pedal in the driver's compartment.
When the accelerator pedal is pushed all the way down, the throttle valve is wide open. The air-fuel mixture
flows freely by the valve, and the engine can produce its greatest power and speed.
The engine is at idle speed when the valve is almost closed and only a small amount of air is allowed to pass
the valve.
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