A vacuum fuel pump, also known as a diaphragm fuel pump, is a type of fuel pump commonly used in motorcycles with carbureted engines. It operates based on the vacuum created by the engine's intake manifold.
Here's a simplified explanation of how a vacuum fuel pump works on a motorcycle:
Intake Stroke: During the intake stroke of the engine, the piston moves downward, creating a partial vacuum in the intake manifold.
Vacuum Signal: This vacuum signal is transmitted to the vacuum fuel pump through a hose or line connected to the intake manifold. The vacuum acts on a flexible diaphragm inside the fuel pump.
Diaphragm Operation: As the diaphragm is subjected to the vacuum signal, it moves downward, increasing the volume within the fuel pump.
Fuel Suction: The increased volume within the fuel pump creates a lower pressure area. This low-pressure zone allows fuel to be drawn from the motorcycle's fuel tank through a fuel line connected to the pump.
Check Valves: The vacuum fuel pump usually contains one or more check valves to ensure that fuel flows in the desired direction. These valves prevent backflow and maintain the proper fuel flow path.
Fuel Delivery: As the diaphragm moves downward, fuel is pushed from the fuel pump and delivered to the carburetor through another fuel line.
Engine Consumption: Once the fuel reaches the carburetor, it is mixed with air and delivered to the engine for combustion during the engine's intake stroke.
By utilizing the vacuum created by the engine's intake manifold, the vacuum fuel pump can continuously supply fuel to the carburetor, ensuring proper fuel delivery and maintaining the required fuel-to-air ratio for efficient engine operation.
It's important to note that with the increasing prevalence of fuel-injected engines on modern motorcycles, vacuum fuel pumps are being replaced by electric fuel pumps, which deliver fuel under pressure directly to the fuel injectors.