Adjust the throttle blade gap to control idle speed. Which parameter is adjusted?

• A. Base idle throttle position
• B. Float Level
• C. Accelerator Pump Circuit
• D. Primary and Secondary Jets

Answer: (A)

At idle, the engine’s speed is governed by how much air can get in through the small opening that remains when the throttle is nearly closed. This opening is set by the base idle throttle position—the position of the throttle blade at idle. Moving the throttle blade to create a larger gap lets more air in, raising idle RPM; closing it reduces air flow and lowers idle RPM. The other parts don’t set idle speed: float level affects the fuel level in the bowl, the accelerator pump circuit handles a surge of fuel during throttle movement, and the jets control fuel metering across throttle positions. Therefore, the base idle throttle position is the parameter that directly controls idle speed.