How car carburetor works

Do you own an antique or classic car? If you do, there’s a good chance it has a carburetor. These days, most modern vehicles use fuel injection systems instead, but back in the day, carburetors were the go-to for managing air and fuel in the engine. Since carburetors aren’t as common anymore, you might be wondering, “What exactly is a carburetor, anyway?” Let’s break it down.

Carburetors explained

Modern car engines use a high-tech system called fuel injection to ensure the perfect mix of fuel and air from the moment you start the car until you turn it off at your destination. But before the fuel-injected engine came along, engines relied on a clever little device called a carburetor—sometimes spelled "carburettor" in other parts of the world, or just "carb" for short.

Carburetors have been around since the late 1800s, thanks to Karl Benz—the man who founded Mercedes. He came up with the first real carburetor design, and it’s been a key piece of automotive history ever since.

So, what does a carburetor do? Its job is to mix the right amount of gasoline and air for the engine to run smoothly. Did you know that gasoline in its liquid form isn’t actually flammable—it’s the fumes that ignite? The carburetor pulls liquid gasoline from the tank, mixes it with air, and sends it to the combustion chamber. There, the spark plug ignites the air-fuel mixture, powering the engine.

However, the air-fuel mix has to be just right. If there’s too much air and not enough fuel (known as “running lean”), the engine might struggle to ignite or even get damaged. On the other hand, if there’s too much fuel and not enough air (called “running rich”), the engine can flood, stall, produce a lot of smoke, or result in poor fuel economy. However, a slightly lean fuel-air mixture can offer better fuel economy, while a slightly rich mixture tends to boost performance.

How carburetors work

Carburetors were a staple in the automotive world for decades and are still a favourite among muscle car and classic car enthusiasts today. Why? Because they’re simple to work on, repair, and replace. No electronics, no computers—just a purely mechanical device that bolts right onto the top of the engine. It’s all cables and vacuum systems doing the work.

The job of a carburetor is to create a fuel and air mixture before sending it to the engine cylinders for ignition, which powers the vehicle. You’ll find it sitting right on top of the engine block, just under the air filter, where it uses vacuum power and cable control to do its thing.

Here’s how it works: The carburetor is connected to the throttle cable, which, in turn, is connected to your gas pedal. When you press the gas, you’re literally causing the carburetor to open up, letting in more air. That extra air pulls in more fuel, creating more power and speed for the engine. Let's break it down more.

Parts of a carburetor

Now that you know what a carburetor is and how it works, let's talk about some of the main parts of one and how each one works:

Venturi

Carburetors come in all sorts of designs and levels of complexity, but the basic idea is pretty simple. Picture a vertical air pipe sitting above the engine cylinders, with a smaller fuel pipe attached to one side. As air flows down the pipe, it has to pass through a narrow section in the middle called a venturi. This narrowing speeds up the air and lowers its pressure, creating a suction effect that pulls fuel in from the side.

Choke valve

So, how do you control the mix of air and fuel? That’s where the carburetor’s two swivelling valves come in. At the top, there’s the choke, which controls the air flow. When the choke is partially closed, less air gets through, and more fuel is sucked in, creating a fuel-rich mixture. This is especially helpful when the engine is cold and just starting up.

Throttle valve

Below the venturi, there’s the throttle plate, which controls the engine’s power. The more the throttle opens, the more air flows through, pulling in more fuel from the side. With extra fuel and air, the engine generates more power and makes the car go faster. That’s why pressing the gas pedal—or twisting the throttle on a motorcycle—makes the car or bike accelerate.

Metering system

This component manages the flow of fuel into the nozzle, making it the key player in getting the air-fuel mixture just right. It includes a fuel discharge nozzle and a metering orifice, working together to ensure precision.

Mixing chamber

The mixing chamber is where air and fuel come together to create the perfect blend before heading into the engine cylinder.

Strainer

A strainer is like a fuel filter, making sure the fuel is clean before it enters the float chamber. It’s made of fine wire mesh that catches dust and other particles. Without the strainer, those particles could clog the nozzles and cause problems.

Float-feed chamber

Now, the fuel supply to the carburetor is a bit more sophisticated than just a pipe. There’s a small fuel tank attached called the float-feed chamber. Inside, there’s a float and a valve that work together to keep the fuel level just right. As fuel flows to the carburetor, the float drops, opening a valve to let more fuel in from the main gas tank. When the chamber is full, the float rises, shutting off the valve until more fuel is needed.

Idling system

The pathway from the float chamber to the venturi tube is known as the idling system. It provides a richer air-fuel mixture when the engine is idling or running at low speeds. This system kicks in when the throttle is open less than 15% or when the car is just idling.

Types of carburetors

Carburetors come in various designs, tailored to fit different engines and serve specific purposes. Here are the main types:

Up-draft carburetor

An up-draft carburetor is designed so air enters from the bottom and flows upward before exiting through the top. The float chamber supplies the fuel, while the venturi creates a pressure difference to help the process along.

Fuel is drawn out of the fuel pipe and mixed with the incoming air to form the fuel-air mixture. This mixture then flows through the throttle valve, which is connected to the accelerator. From there, it heads into the engine cylinder, where combustion takes place.

Down-draft carburetor

The down-draft carburetor is the most popular type, and for good reason. It became more commonly used during the late 1930s. It pulls air into the mixing chamber from the top instead of the bottom, and it comes with some great advantages:

• Gravity helps the fuel-air mixture flow, which means the engine performs better at lower speeds, especially under a load.
• Its position is easy to access for maintenance and adjustments.
• It helps the engine achieve better volumetric efficiency, meaning it can take in more air and fuel for improved performance.

Horizontal or side carburetor

The horizontal carburetor works much like a down-draft carburetor, but it’s positioned horizontally. It’s pretty straightforward—air flows in from one end, mixes with fuel inside the carburetor, and then heads into the engine cylinder for combustion. Side carburetors were more commonly used in Europe.

Multi-barrel designs

The simplest carburetors are “single barrel,” meaning they have just one venturi doing all the work. But for more power, you’ve got “double barrel” or even “quad carbs,” with two or four venturi working together.

Why the extra barrels? Bigger engines need more fuel to generate power. In some cases, like with four-barrel carburetors, the barrels are designed to work progressively. The two “primary” barrels handle most of the job, while the two “secondary” barrels kick in at higher speeds or when extra power is needed. This setup helps save fuel when the extra boost isn’t necessary but delivers plenty of power when you need it. It was commonly used in V8 engines.

Advantages of carburetors

Carburetors have been a staple in internal combustion engines for decades, especially in older vehicles and small engines like those in motorcycles and lawnmowers. While modern engines have largely moved to fuel injection systems, carburetors still have some clear advantages:

• Carburetor parts are generally cheaper than fuel injection components.
• They do a great job creating the right air-fuel mixture for combustion.
• Carburetors can deliver a powerful and precise mixture to the engine.
• The engine isn’t limited by how much gas is pumped from the tank, meaning the cylinders can pull in more fuel through the carburetor, resulting in greater power and a denser mix in the combustion chamber.

Disadvantages of carburetors

While carburetors have their perks, they also come with some downsides, especially when compared to modern fuel injection systems. Here are the main drawbacks:

• At very low speeds, the fuel-air mixture can be too weak, causing ignition issues.
• Changes in atmospheric pressure can affect how the carburetor performs.
• Carburetors tend to use more fuel compared to fuel injectors.
• They produce more air pollutants than fuel injection systems.
• Carburetors require more upkeep to keep them running smoothly.

How to maintain a carburetor

Taking good care of your vehicle's carburetor is crucial for keeping your engine running smoothly and efficiently. Here are some important car maintenance tips to keep your carburetor in great shape:

Clean it regularly

Over time, dirt, debris, and varnish can build up inside your carburetor, clogging passages and hurting performance. A good cleaning with a carburetor cleaner can clear out those deposits and keep fuel and airflow running smoothly.

Inspect it for damage or wear

Take a look at key components like the throttle valve, float, and jets to check for wear or damage. If anything seems off, replace it to avoid issues like fuel leaks, rough idling, or sluggish acceleration.

Adjust the settings periodically

Fine-tuning your carburetor—like adjusting the idle speed and air-fuel mixture—can make a big difference in how your engine runs. Follow your vehicle's service manual or get help from a trusted mechanic to make sure everything is set just right.

Use high-quality fuel

Stick to high-quality fuel and consider using additives to keep your carburetor clean. Avoid storing fuel for too long since stale gas can cause gumming and lead to carburetor and engine problems.

What is modern fuel injection?

These days, nearly every new car comes with an electronic fuel injection system—and for good reason. Fuel-injected engines are more fuel-efficient and produce fewer emissions. The big shift toward fuel injection started back in the 1980s when computer chips became small and affordable enough to use in everyday vehicles.

Here’s how it works: a fuel-injected engine relies on a computer to figure out the perfect mix of air and fuel for the engine at any given moment. Sensors constantly gather data, like the engine’s temperature, the current fuel mixture, and the oxygen level in the intake air. The computer uses all this information to fine-tune the mix, ensuring the engine runs efficiently and smoothly. It’s a smart system that takes the guesswork out of balancing performance and efficiency.

Contact BrokerLink today

Proper maintenance is important to keep your carburetor and car engine running smoothly, and having the right car insurance is just as important. If you want to learn more about how having the right car insurance coverage could protect your antique or classic car, reach out to BrokerLink today. One of our licensed insurance advisors would be happy to answer any car insurance questions you have.

You can reach us by phone, email, or in person at any one of our locations throughout Canada. No matter how you choose to get in touch, a BrokerLink insurance advisor will be happy to assist you. We also encourage you to take advantage of our free online quote tool that can provide you with a competitive quote in minutes.

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