Carburetor vs. Fuel Injection: What’s the Difference?

If you’re coming to powersports with limited mechanical knowledge, a common question may cross your mind: what’s the difference between a carburetor and fuel injection? 

Whether you’re talking about motorcycles or cars, the two primary delivery systems to combine fuel and air with the fire necessary to induce combustion and drive pistons inside cylinders are the same. Here’s a quick guide to the difference between carburetors and fuel injectors.

How Does a Carburetor Work?

The carburetor brings two of the key elements of combustion — fuel and air — together so they can be delivered into the combustion chamber. 

While carburetors may be distinguished by how many barrels they have (generally between one and four), there’s another way carbs are separated. They can be downdraft, side draft, or updraft carburetors. This describes how the air flows through the carburetor: from above, the side, or below.

Carburetors work on the same Bernoulli principle that explains how an airplane wing generates lift. Basically, rapidly flowing fluids (or gases) exert lower pressure than slower flowing fluids. In a carburetor, air is drawn into the barrel and moves into a narrow area known as a venturi. As the air moves faster, it creates lower pressure, which draws fuel out of the carburetor jet. 

Behind the jet is a float bowl, where the fuel waits to be expelled through the jet. The float bowl determines how much fuel should move through the jet and into the venturi area of the carburetor. At the bottom of the entire assembly is a throttle plate that opens and closes. When the operator of the engine opens the throttle by twisting it on a motorcycle or hitting the pedal in a car, the throttle plate opens more and allows more fuel and air to reach the engine.

And when the throttle is closed and the engine is idling, an idle jet sends a small amount of fuel into the cylinder to keep the motor running even when the throttle isn’t open.

How Does Fuel Injection Work?

More common in modern vehicles, fuel injection uses high pressure to atomize the fuel to mix it with air for combustion. 

There are three basic types of fuel injection: 

• Direct fuel injection: Sprays the fuel straight into the combustion chamber. 
• Ported fuel injection: Sprays the fuel into an intake manifold outside the valve where it awaits valve opening and introduction into the cylinder. 
• Throttle body fuel injection: Uses a single injector to mix the fuel in the throttle body before it travels into the cylinder.

In an electronic fuel injection system, an electronic control unit (ECU) controls the process. A fuel pump pulls the fuel from the tank, and a pressure regulator keeps the fuel pressure in line with the intake pressure. The ECU then controls how much time the injector stays open, a duration known as the pulse width. As for the mechanical opening and closing of the injector, it’s handled by a solenoid and a plunger. 

The exact duration of the opening and closing is based on a variety of readings from voltage, mass airflow, oxygen, and manifold absolute pressure sensors. Multi-port injectors can open and close individually, and the ECU also controls idle speed through a throttle control system.

Fuel Injection or Carburetor?

A carburetor offers simplicity. Cleaning, rebuilding, or replacing a carb are all fairly straightforward. On the other hand, fuel injection systems can be more difficult to maintain because of their reliance on an ECU for control. However, cleaning the fuel injectors on a motorcycle improves the performance of your engine and is worth the time and effort it takes to get it done.