What Is the Difference Between a Lean and Rich Carburetor Mixture

Pit Shop Auto Repair can attest that subtle things can really affect your vehicle’s engine performance. One of these subtle things in the air and fuel being mixed in the carburetor. The wrong air/fuel ratio can stall your car, truck, crossover, or SUV or make it impossible to start. Let’s talk about lean and rich carburetor mixes and how they affect your vehicle’s performance and gas mileage.

Air, Fuel, and the Combustion Chamber

In very basic terms, your automobile needs air and fuel in the combustion chamber to start and run. The carburetor mixes the air and fuel into the proper ratio, and the spark plugs generate a spark to ignite the mixture. It’s this ignition and combustion that gets the engine started and running. This is a very basic description of what happens when you start your car, but it’s perfect for the purposes of this blog post.

Lean vs. Rich Mixtures

If your carburetor is not adjusted properly, you might end up with too much air in the air/fuel mixture, and we call this a “lean” air/fuel mixture. Additional problems that can cause a lean carburetor mixture include issues with the fuel system, such as a clogged fuel filter, dirty fuel injectors, or a dying fuel pump; a dying oxygen sensor; or a dying mass airflow sensor. Lean means your vehicle is fuel-starved.

If you have too much gasoline in the air/fuel mixture, this is what is called a “rich” air/fuel mixture. Strangely, one of the problems in the fuel system that causes a lean mixture can also cause a rich mixture. If your fuel injectors are dirty and stuck in the open position, gas will pour into the carburetor, gorging the carburetor and combustion chamber with fuel, i.e., your vehicle is fuel-stuffed.

Problems With the Mixtures

In either case, you are going to notice trouble when try to start your vehicle and when it runs. For example, you might not be able to start your automobile if there isn’t enough gas in the air/fuel mixture or if the excess gas is flooding the engine. You may also notice performance issues, such as stalling because it’s fuel-starved or surging because it’s fuel-stuffed. A carburetor adjustment can usually fix these problems.

Stop by Pit Shop Auto Repair in Libertyville, IL, if you think your vehicle’s air/fuel mixture is off.  We’ll let you know if we can see you right away or if it’s better to schedule an appointment.