At what engine speed does the main metering jet function effectively in a float-type carburetor?

The main metering jet in a float-type carburetor is designed to function effectively at all speeds above idle range. This is because the main metering jet is responsible for supplying the majority of the fuel to the engine during higher operational speeds where the demand for fuel increases significantly.

At idle speeds, the fuel-air mixture is primarily controlled by the idle jet and other low-speed circuits, which ensure optimal performance at those lower engine RPMs. As the engine speed increases, the airflow through the carburetor also increases, necessitating the role of the main metering jet to provide adequate fuel for combustion. The main jet operates effectively as it adjusts the amount of fuel based on the increased airflow, ensuring optimal engine performance during acceleration and higher speed conditions.

Thus, the main metering jet really comes into play and provides the necessary fuel supply as the engine transitions from idle to various higher speeds, making it critical for overall engine efficiency and power delivery during normal driving conditions.