This lever is a crucial manual control for engine operation and safety.
RUN Position: In this position, fuel flows freely from the pump to the injectors. The engine is allowed to operate normally.
STOP Position: Moving the lever to "Stop" does not shut off an electrical circuit like in a car. Instead, it mechanically actuates a valve inside the pump that blocks the flow of fuel to the injectors. With no fuel supply, the engine stops. This is the primary method for shutting down a mechanical PT-powered engine.
Important Note: Some setups have an optional "AIR FUEL" position, which is used for priming the system after running out of fuel or performing filter changes.