What is the purpose of the idle circuit in a carburetor?

The purpose of the idle circuit in a carburetor is to allow just enough fuel to keep the engine idling. At low speeds, when the throttle valve is nearly closed, the engine requires a leaner fuel mixture to run smoothly without stalling. The idle circuit delivers a specific amount of fuel mixed with air, ensuring the engine can maintain a steady idle without overloading the engine with too much fuel. This system is crucial for ensuring that the engine remains operational during idle conditions, which is particularly important for starting and stopping the engine, as well as transitioning from idle to higher speeds.

The functionality of the idle circuit is significant in maintaining engine performance at low RPMs, which is essential for smooth operation and engine longevity.