Carbureted vs. Fuel Injected Systems


Filed Under (Tips and Review) by admin on 25-10-2010

fuel injection (FI) systems have been around since the 1950′s and became widely used in cars during the 80′s. By the 1990′s all cars sold in the United States were equipped with FI systems, and though motorcycle manufacturers have included FI systems with some models as early as 1982, it isn’t until recently that the industry has seen wide spread use of FI. Since a lot of people come into my shop with questions about FI, I thought I would point out some of the differences between FI and carbureted systems as well as the benefits and disadvantages of both. A carbureted system is a mechanical system using air pressure to control the flow of fuel through the system. There are three basic parts in a carburetor, the throttle valve, the venturi and the float bowl. The throttle valve controls the amount of air that flows into the throat of the carburetor also known as the venturi which is simply a tapered hole through the carburetor body. As the venturi narrows, air moving through it is forced to speed up creating low pressure inside the carburetor. In a siphoning effect as the air tries to equalize the pressure, fuel is drawn in from the float bowl mixing with the air before entering the engine. The wider open the throttle valve, the more air will flow, drawing more fuel. A number of circuits are built into the carburetor in order to control the amount of air/fuel being drawn into the engine. In this context a circuit refers to a fuel passageway as opposed to an electrical circuit. In fact, nothing electrical controls fuel delivery in a carbureted system, it is all based on fluid flow, vacuum and hydraulics. The different circuits represent various throttle positions such as idle, partially open and fully open, and each of these circuits can be tuned to modify the efficiency of fuel delivery to the system. Fuel injection (FI) systems, on the other hand, rely on an electronic fuel pump to deliver fuel. The fuel pump delivers fuel at around 50psi as opposed to carbureted systems at normal atmospheric pressure of about 15psi. When the fuel reaches the injectors, the higher pressure allows much finer atomization (creating mist) of the fuel. The injectors then spray the atomized fuel into the intake manifold in a uniform conical pattern. The uniform pattern and fine atomization of the fuel spray increase the efficiency in which it is burned