What is a Carburetor & How Does it Work?

The engine is a most important part of a vehicle. The amount of air and fuel required by an engine varies according to the vehicle model, the operating speed, and various other factors. The latest diesel engines have an electronic control system known as fuel injection.

The petrol engine has a carburetor (spelled “carburettor or carburator“). A carburetor is a device that supplies a mixture of air and fuel to a spark-ignition engine. This article mainly explains the working, types, and many other aspects of the carburetor.

What is a Carburetor?

A carburetor is part of an internal combustion engine that is used to mix and control the air and fuel entering the engine cylinder. In simple words, a carburetor is a tube that sucks fuel and air through valves, mixes them, and sends this mixture to the engine cylinder to drive the vehicle.

The main function of the engine is to generate power by burning the air-fuel mixture and driving the vehicle.

A carburetor is known as the “heart” of a vehicle engine. When the “heart” doesn’t work properly, you can’t expect the engine to work properly or can’t get adequate power. If the engine doesn’t work properly, your vehicle couldn’t run smoothly.

The carburetor first sucks air from the environment, mixes it with an appropriate amount of fuel, and sends this mixture into the engine cylinder of the IC engine.

The carburetor has an accelerator pump, venturi tube, main jet, idle (or slow speed) jet, a choke, and a liquid fuel storage chamber.

A valve uses to control the amount of fuel in the storage cylinder. A float uses to operate this valve. The choke uses to reduce air intake and permits a fuel-rich charge to enter the cylinder when starting a cold engine.

When the engine heats up, the choke opens automatically or manually or by engine speed and temperature controllers.

The latest automotive cylinders have fuel injection systems instead of carburetors. These systems supply fuel more efficiently, use a low amount of fuel and reduce pollution. However, carburetors are still used in old motorcycle engines, car engines, compact chainsaws, and lawnmowers.

How Does a Carburetor Work?

Carburetors were used for decades in the automotive industry, and are still often preferred today in muscle cars and other classics because they’re easy to work on, repair and replace. It’s an entirely mechanical machine with no electronics or computers at play, and it bolts right onto the top of the motor. In terms of operation; just cables and vacuum systems control the carb’s mechanism.

Carburetors are used to mix fuel and air together before sending the mix into the engine cylinders for ignition, powering the vehicle. The carburetor sits atop the engine block beneath the air filter, and operates using a combination of vacuum power and cable control.

The carburetor is attached to the throttle cable, which is attached to the gas pedal. When you push down on the gas, you’re literally causing the carburetor to open up and pull in more air, thus pulling in more fuel as well, bringing more power and speed out of the engine.

To get slightly more technical, air is pulled through a “venturi”, or bottleneck, in the carburetor. This speeds up the air’s velocity and creates a vacuum. That vacuum pulls fuel from a float chamber or reservoir into the jet, where it mixes with air, flows into the cylinder where a spark plug is fired.

That causes the fuel-air mix to ignite, which pushes the piston and – in purely technical terms – makes the car go vroom-vroom.

That whole process starts with the carburetor, which has led some to call it “the heart of the engine.”

Read Also: Different Types and Working of Petrol Engine

Parts of Carburetor

The car carburetor has the following major components:

1. Throttle valve
2. Venturi tubes
3. Strainer
4. Metering system
5. Mixing chamber
6. Idling system
7. Float chamber
8. Choke valve

#1. Throttle Valve.

The throttle valve is one of the major parts of your vehicle’s carburetor. The throttle valve regulates the amount of the air-fuel mixture delivered to the engine cylinder. As you press the car accelerator, the throttle valve opens.  

Read More: Bad Throttle Body Symptoms and Causes

#2. Venturi Tube.

Venturi tubes are hollow tubes whose cross-section gradually decreases and whose smallest area is at the throat. This tube assists in reducing the float chamber’s air pressure. The air enters at a low speed, but when it leaves the venturi tube, its pressure becomes very low while velocity highly increases.

#3. Strainer.

A strainer filters the fuel before sending the fuel into the float chamber.  

The strainer has a fine wire mesh that cleans the fuel by eliminating dirt and other suspended matter. If it doesn’t remove these dirt particles, the dirt particles may clog the nozzle.

#4. Metering System.

This part of the carburetor regulates the fuel flow into the nozzles. The metering system has a responsibility to make a fuel-air mixture according to desired air-fuel ratio.  

This system has the following two major parts:

1. Fuel discharge nozzle
2. Metering orifice and

As the air passes by the venturi tube, it creates a low-pressure field at the throat. This pressure difference causes the fuel to flow in the air stream.

The amount of fuel is controlled by the metering orifice and the discharge hole located at the outlet of the fuel drainage nozzle.

#5. Mixing Chamber.

This chamber uses to mix the fuel and air. After the mixing process, the fuel-air mixture is delivered to the engine combustion chamber.

#6. Idling System.

This system has a direct passage from the float chamber to the venturi. It has a responsibility to deliver a rich air-fuel mixture at a slow speed and during idling. The idling system activates when the idle speed or the throttle opening is less than 15%.

#7. Float Chamber.

This chamber works as a fuel storage tank to supply fuel to the engine. The float chamber has a float valve to maintain the fuel level inside the chamber.

As the fuel level in the float chamber becomes lower than the fixed level, the float moves down and opens the fuel supply valve. As the fuel supply valve opens, the fuel starts to enter the float chamber.

When the fuel level becomes equal to the required level, the float moves up, closes the valve, and stops the fuel flow.

#8. Choke Valve.

The choke valve uses to regulate the air-fuel mixture. This valve only controls the amount of air in the mixing chamber.

This valve is usually in a half-open and half-closed position. When the engine needs a rich mixture, you press the choke valve. This valve stops the airflow into the chamber so that the engine can receive the rich fuel-air mixture.  

In winter, when the engine does not start, this valve is used to deliver a rich fuel-air mixture to the engine cylinder. In this way, the air-fuel mixture burns quickly, and the engine starts.

Types of Carburetors

The carburetor has the following major types:

1. Down-draft Carburetor
2. Up-draft type carburetor
3. Horizontal Type Carburetor

#1. Down-draft Carburetor.

In the down-draft carburetor, fuel is supplied from the mixing chamber base, and the air is supplied from the top of the carburetor.

The down-draft carburetors work on the same principle as the up-draft carburetors. In this type, the fuel also comes from the fuel pipe due to pressure differences. As the desired quantity of air and fuel comes into the mixing chamber, the air and fuel mixing process occurs.

A choke valve uses to control the produced air-fuel mixture, and a throttling valve uses to regulate the air-fuel mixture supply to the engine.

Read Also: Different Types of Diesel Engines

#2. Up-draft type Carburetor.

In the up-draft type carburetors, the air is supplied from the base of the carburetor, and fuel is provided by the float chamber.  

As the pressure difference produces between the venturi tube and the float chamber, the fuel leaves the float chamber with the help of the Venturi tube and mixes with the intake air, and the metering system makes a flow-air mixture.

The throttle valve opens as the driver presses the accelerator, and the fuel-air mixture enters the engine chamber. As the mixture enters the combustion chamber, the fuel combustion process starts, and power is produced to run the vehicle.

#3. Horizontal Type Carburetor.

As you turn the down-draft carburetor horizontally, it converts into a horizontal carburetor.

In these types of carburetors, air enters from one side of the carburetors. After fuel and air entry, the mixing chamber mixes air with fuel to form an air-fuel mixture. This produced mixture is sent to the combustion chamber for producing power.  

Read Also: Different Types of Reciprocating Engines

How to Clean a Carburetor?

Follow the below-given steps to clean your carburetor:

1. Detergent dilution: Use a detergent to clean the carburetor. Mix the diluted detergent in a large tank. But you must use a non-corrosive detergent that can’t damage the rubber or plastic parts of the carburetor.
2. Use of Bleach: Don’t use a vinegar, as acetic acid can make metals more prone to oxidation. Also, do not use bleach, as sodium hypochlorite (bleach) attacks metals such as aluminum and steel and damages the rubber seal.
3. Clean the air filters: Before cleaning the carburetor, clean the air filters and ensure that the air entering the carburetor contains no dust and other contaminations. To clean the filters, detach the spark plug wires (if equipped) and turn off the fuel supply. Remove the casing and wing nuts connecting the filter, and remove the external components. Use an air blower to blow air into the filter and remove the dust.
4. Detach the carburetor: Use a screwdriver and pliers to detach the covers and guards, as well as the hoses and linkage. You must also need to remove all other clamps or cover that fix the carburetor in its place. Also, disconnect the hose clamps connecting the fuel line to the carburetor. After all these processes, detach the carburetor and use a blower to blow compressed air to remove dust from its housing.
5. Removal of the carburetor float: Detach the fastening screws of the carburetor float (bowl-shaped container) and make sure that no residual gas is sprayed in the float (dispose of properly). Remove the pin that rotates the float and keep it in a safe place. Then detach the float by pulling it directly from its housing.
6. Remove all other detachable parts: Remove all other detachable parts of the carburetor for its cleaning. Remember the position and location of all the removable parts so that you can easily reinstall them at their exact locations.
7. Soak and Scrub Parts: Soak the carburetor float and other parts in a large tank of diluted detergent and let them immerse for up to 8 minutes. Wash all plastic parts using a stiff nylon brush and metal parts using a brass brush. Be sure to clean the small ventilation holes. You must also use the diluted detergent solution to clean the other small parts.
8. Rinse and Dry: Rinse all the parts of the carburetors by using a clean water bowl and dry them completely. To remove extra water, use a blower to blow dry compressed air from the small holes and vents.
9. Reassembly and replacement: Carefully reassemble the carburetor and secure it to the engine. Reconnect all cables, clamps, gaskets, and hoses in their locations.

Read Also: Working of Power Steering System

Benefits of Carburetors

While most modern vehicles use fuel injection systems, carburetors offered several benefits that made them a crucial component in internal combustion engines. These include:

• Simplicity: Compared with electronic fuel injection systems, carburetors have a basic design that is easy to understand and manufacture.
• Cost-effective: Due to their simplicity, carburetors have lower production costs than fuel injection systems.
• Easy to maintain: With their straightforward design, carburetors are relatively easy to maintain and repair and most issues can be addressed with basic mechanical skills without the need for specific diagnostic equipment.

Cons of Carburetors

There are disadvantages to using carburetors, which have led to their replacement by more modern fuel injection systems (which you’ll learn about in a minute). Drawbacks to using carburetors include:

• Inefficiency in fuel delivery: Carburetors can have issues delivering the right amount of the air-fuel mixture needed for optimal engine performance, unlike fuel injection systems that can adjust fuel delivery in real-time based on sensory inputs.
• Susceptible to environment: Environmental factors such as temperature and altitude changes can negatively impact carburetor performance and, in turn, affect engine performance and efficiency.
• Frequent maintenance: While carburetors may be easy to maintain, they do require regular maintenance to function correctly, which can be time-consuming. Components can become clogged or simply wear out relatively quickly compared to fuel injection systems.
• Emissions control challenges: Compared to fuel injection systems, carburetors are less effective when it comes to controlling exhaust emissions.

Carburetor vs. Fuel Injection

Carburetors were invented in 1888 by Karl Benz, one of the founders of Mercedes-Benz. It was a groundbreaking development for the industry at the time, and the technology was used by car manufacturers up until the late 1980s, when carburetors began getting replaced by fuel injection systems.

The main difference between carburetors and fuel injection systems is that fuel injection systems introduce an electronic process for delivering the necessary mixture for combustion.

While modern injection systems began being widely used in the 1980s, NASCAR vehicles still featured carburetors until 2012.

Fuel injection systems feature a range of parts that include a computer, fuel injectors, oxygen sensors and pressure regulators that work to ensure the right blend of air and fuel is delivered to the combustion chamber.

Electronic fuel injection allows for precise control over the amount of fuel being pushed into the cylinders. Fuel exits the fuel tank, traveling through lines toward the engine.

There is also the electronic control unit (ECU), which determines the exact amount of fuel the engine needs based on the volume of air entering the engine and the optimal air/fuel ratio determined by the specific manufacturer.

The main difference between the carburetor and fuel injection system is given below:

Carburetor	Fuel Injection
The carburetor first mixes the air and fuel and then sends the air-fuel mixture into the engine cylinder.	In a fuel injection system, the air and fuel mixing process takes place after their entry into the engine.
It is designed by using conventional technology.	It is designed using the latest technology.
In winter, the carbureted vehicle is very hard to start.	Fuel injection-based vehicles have an easy start-up, even in a cold climate.
It works for a long time if you properly maintain it.	A properly maintained fuel injection system also has a long service life.
The carbureted vehicles generate more emissions than fuel-injected vehicles.	The fuel-injected vehicle generates very low emissions.
The carburetor has a low cost.	The fuel injection systems are expensive.
It doesn’t have superior features as a fuel injector.	It has excellent features such as low fuel economy and emission rate.
It can’t adjust the air-fuel ratio according to the engine condition.	It has the capability to adjust the air-fuel ratio according to the engine requirements.
The carburetor wastes more fuel than the fuel injection.	The fuel injector wastes a very low amount of fuel.
It has simple cleaning and maintenance.	It has complicated cleaning and maintenance.
This system requires very low maintenance.	It requires regular and high maintenance.
The carburetors are most commonly used in petrol engine vehicles.	The fuel injection systems are most commonly used in diesel engine vehicles.

Carburetor vs. Throttle Body

There is sometimes confusion surrounding the differences between a throttle body and a carburetor. Both are components that manage the air and fuel entering the engine, but they operate differently and with different technologies.

Carburetors have the primary function of mixing fuel and air in the correct ratio before they enter an engine’s combustion chambers. The throttle body, on the other hand, helps to control the amount of air entering the engine and doesn’t mix fuel with air – this is done separately by fuel injectors within a modern fuel injection system.

Carburetors use mechanical means for the process, while the throttle body works in conjunction with an electronic fuel injection system.

Carburetors are still found in small engines, motorcycles and classic cars, whereas you can find a throttle body in more modern automotive engines or for industrial and high-performance applications.

Signs of a Failing Carburetor

Although newer vehicles aren’t being produced with carburetors, there are older models on the road that still have them.

If you happen to be driving a car that has a carburetor, it’s important to know some of the signs that it might be failing. Over time, wear and tear can occur to the carburetor, and it might need to be serviced or replaced. Some symptoms include:

• Reduced engine performance: The most common sign something’s wrong with the carburetor would be reduced engine performance. The carburetor wearing down can cause the air-fuel mixture to be off, resulting in a decrease in acceleration and power.
• Backfiring/overheating: These are also common symptoms of carburetor failure. A lack of fuel in the air-fuel mixture can cause these two issues to happen, which in severe cases can cause severe engine damage.
• Black exhaust: There should never be black smoke coming from the exhaust! This is likely a sign that the engine is using too much fuel, also known as fuel-rich. This can come from a carburetor that is worn and delivering excess amounts of fuel.
• Difficulty starting: A common problem stemming from a worn carburetor is hard starts or difficulty starting the engine. Issues messing up the air/fuel ratio can result in these problems.

If you experience any of these issues, it’s a good idea to take your vehicle to a trained technician who can diagnose and fix your problem. You don’t want to cause more damage to your engine by ignoring possible signs of carburetor failure!

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