How a Fuel Pulse Pump Works

by Ezmeralda Lee


If an engine is to work correctly, fuel needs to be delivered continuously and in fixed proportions to the engine. This is the function of a well maintained fuel pulse pump. With the use of pulses, a pre-defined quantity of fuel is delivered to the engine in a steady stream

The Components

A pulse fuel pump has four tubes connected to it. One tube connects the fuel tank. Two tubes connect each carburetor and one tube connects the crankcase of the engine. When the engine revolves, the tube connecting the engine delivers fuel with a pulse of pressure at each revolution. The diaphragm pulsates with the pressure. At the top of the pump are two chambers. They are separated by a pair of one way valves. These valves ensure that the fuel that passes through does not come back. Fuel flows from one chamber to the other at one pulse and at the next pulse, fuel moves to the engine. A well maintained pump works at 5,000 pulses per minute.


The bottom end of the engine crankcase is continuously subjected to a high or low pressure with every pulse. This pulse is transferred to the fuel pump by a pulse tube. The pulse line connects the pulse chamber. The pressure of the crankcase is pushed by the pulse through a pair on one way valves and fuel passes continuously, and in a correct measure, to power the engine.


A pulse fuel pump has its own limitations. One cannot estimate the fuel pressure capacity while going uphill. The fuel is likely to rise when the vehicle climbs. The amount of fuel is always limited to the pressure or pumping value of the crankcase. It is impossible to create too much pressure with a pulse pump for the carburetors float level. Pressure of the pump slowly decreases as the crank seals and gaskets begin to leak over time.


The pump should be mounted, keeping a distance away from the crankcase. If the pump is close to the crankcase, the pulse tube could become damp and the efficiency of pumping fuel will be greatly reduced. The pump should never be mounted on the crankcase of the engine. This is because the engine vibrates. The vibration of the engine will affect the pulsating flow of fuel and the regulated flow of fuel enabled by the pump will be affected. The pulse line must be rigid enough to avoid becoming damp. The best way to mount the pump is to place it higher than the engine. This will ensure that fuel from the engine will not be able to flow back into the chamber of the pump.

Types and Their Functions

Rectangular pulse pumps are used for single carburetor applications. Round pumps are the more commonly used pumps and are used for large volumes of fuel feeding two carburetors. The 2-stroke engine pulse is connected to the crankcase of an engine. The 4-stroke engine contains lubricating oil and the pulse tube of the pump is connected to intake manifold of the engine.

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