What Is a Carburetor and How Does It Work?

Photo by christian buehner

Originally Posted On: What Is a Carburetor and How Does It Work? | Autotent

You’ve probably seen this in a dozen movies or television shows: the main character wakes up, hops in their car, turns the key, and… nothing. The car won’t start.

They get the vehicle hauled to a workshop. After popping the hood and taking a look around, the mechanic nods sagely and says, “Well, there’s your problem: your carburetor’s shot.”

For many of us, that’s the only time we think about a carburetor–as a piece of mechanical jargon used to explain away car troubles. It’s no different than a sci-fi character saying their ship’s hyperdrive is malfunctioning.

Unlike a science fiction spaceship, though, a carburetor is a real car part that is critical to keeping your vehicle running. With that in mind, it’s a good idea to learn a bit about carburetors and why they’re important.

Read on to learn more about carburetors–how they work, how they’re built, and what makes them so crucial to a car’s operation.

To understand a carburetor’s function in a car, there are a few things you need to know about the workings of a gasoline engine. Gasoline engines work via the process of combustion.

Combustion is the process of burning fuel to release heat energy. In a car, this energy is then used to propel the vehicle. However, for fuel to burn properly, it needs air.

The issue is that you need a specific amount of air in order to burn the fuel in an engine properly.

If you have too much air for the amount of fuel you have, it’s called burning lean. On the other hand, too little air is called burning rich. Both affect how your car runs.

A small variation in either direction isn’t a problem; in fact, a lean burning engine can help your fuel economy and a rich burning engine can help your performance.

Too much or too little air, though, and you can cause significant damage to your engine.

That’s where a carburetor comes in.

The carburetor’s job is to ensure that the engine has the right mix of air and fuel. Using a series of valves and chambers, carburetors inject the proper mixture into a car’s engine.

There are a few different styles of carburetors, but all of them work using the same basic principles. They connect to the engine’s metal cylinders and use vacuum power to draw fuel and air where they need to go.

The most basic form of a carburetor is a vertical air pipe joined to a horizontal fuel pipe.

When the carburetor is active, air travels down this vertical pipe. The air passes through a kinked section partway down, which changes the air’s pressure, which in turn causes a vacuum effect.

That vacuum then pulls fuel in from the horizontal fuel pipe. That explains how the fuel and air mix, but there’s still the issue of getting exactly the right ratio of each.

A pair of valves control this ratio. One valve sits above the vertical pipe’s kind, while the other sits below. The former controls how much air goes into the engine.

The second, lower valve serves much the same function. The only difference is that this one affects the amount of fuel entering the engine as well.

A carburetor is not the only way to supply a fuel and air mixture to an engine. Many newer models rely on fuel injection systems, but classic vehicles still rely on carburetors.

A carburetor is composed of many parts, even beyond the simple pipe structure described above. The pipe has multiple interior components and connects to a small fuel chamber.

When air first enters the pipe, it passes through a filter. From there, it moves through the valve we discussed earlier, which is called a choke. After the choke is the kinked portion that creates the vacuum; this is called a venturi.

Connected to the venturi is the fuel pipe, which is in turn linked to a float-feed chamber.

The float-feed chamber is a miniaturized fuel tank; the chamber stores a small amount of fuel as an intermediary between the carburetor and the car’s main fuel tank.

A float-feed chamber has a small float attached to a valve. When the chamber is full, fuel buoys the float and keeps the valve closed. As fuel moves from the chamber to the engine, the float falls and the valve opens.

When the valve opens, more fuel can enter into the chamber, filling it back up. Like the air at the top of the pipe, the fuel also passes through a filter before entering the chamber.

Once fuel and air pass through the venturi, they hit the second valve in the main pipe, called the throttle. After passing through the throttle, they reach the engine cylinders.

As mentioned earlier, you can make small alterations to the air and fuel ratio of a car to produce different effects. For many car enthusiasts, tuning a carburetor for increased performance is a must.

Acceleration and top speed are the main areas that carburetor tuning affects. That said, the first thing to address with tuning should be your idling speed. This acts as a base for future fine-tuning.

Making carburetor adjustments is fairly simple. All you need to do is adjust the idle speed and idle mixture screws. These adjustments are usually made while the car is running, though, so you need to be very careful.

Don’t touch anything hot, and keep your fingers away from the carburetor opening and the engine fan. You should also wear safety gloves and goggles.

Different carburetors will have their screws in different areas, so be sure you have a firm grasp of your carburetor before attempting this!

It’s also worth noting that many carburetors will need to be adjusted consistently for the best performance. There are exceptions, though: the Edelbrock 1406 is able to maintain calibrations much longer than most carburetors.

Now that you know what a carburetor does, you can see how important it is for your vehicle. While not every car has a carburetor these days, it serves a critical function in the cars that do have one.

Do you have questions about other car parts? Check out our auto technology section for more information and advice!