What causes a single diaphragm acceleration pump to discharge fuel?

The discharge of fuel from a single diaphragm acceleration pump is primarily caused by an increase in manifold pressure when the throttle is opened. When the throttle is opened, the engine demand for air increases, leading to a corresponding increase in air and fuel flow into the engine. This action creates a vacuum in the intake manifold, allowing the diaphragm in the pump to flex and push the fuel into the intake system.

This response of the diaphragm is crucial for providing an immediate supply of fuel, particularly during quick acceleration when the engine demands additional fuel to match the increased air intake and prevent a lean mixture. By ensuring that fuel is delivered in accordance with the manifold pressure changes, the acceleration pump plays a vital role in maintaining engine performance and responsiveness during throttle movements.