When an engine operates correctly and creates satisfactory power under load but not at partial load, the __________ are not at fault.

When an engine is functioning properly under load but struggles at partial load conditions, it suggests that the components responsible for managing fuel and air delivery at lower speeds and loads may be the ones at fault. The correct choice points to the main jet, fuel supply, and high-speed air bleed.

The main jet is primarily involved in providing fuel at higher throttle positions; therefore, when the engine is under load, it efficiently delivers the necessary fuel. The fuel supply ensures that there is a sufficient amount of fuel available to meet demand during full load conditions. The high-speed air bleed assists in the atomization of fuel in higher RPM range, which is crucial for performance at full load.

In contrast, issues related to the pilot jet, low-speed air bleed, and other related components usually stem from problems that occur at lower engine speeds or throttle positions. Since the engine performs well under load but not under partial load, it indicates that the components that primarily function during partial throttle are likely where the problem lies. This helps clarify why the other options do not address the issue accurately; they include elements that are more relevant to partial or low-load conditions.