What supplies fuel during cruising and wide open throttle?

The correct answer is the main jet, which plays a crucial role in fuel delivery during cruising and wide-open throttle conditions. The main jet is designed to supply the engine with the appropriate amount of fuel at higher RPMs and when the throttle is fully open.

At these operating conditions, the fuel-air mixture becomes richer, requiring a larger volume of fuel to maintain optimal combustion efficiency and engine performance. The main jet operates in conjunction with the throttle valve to ensure that as more air is drawn into the engine, sufficient fuel is supplied to match the increased demand. This is critical for achieving maximum power output and smooth operation while accelerating.

In contrast, other components mentioned do not fulfill this function during high-demand situations. The slow jet, for example, provides fuel during idle and low throttle settings, while the choke valve is typically used only during startup to enrich the mixture for cold engine operation. The throttle valve regulates airflow but does not supply fuel directly. Understanding the role of the main jet is essential for grasping how fuel delivery systems work in relation to engine performance under various operating conditions.