What Is the Main Function of a Carburetor?

The main function of a carburetor is to mix and meter air and fuel into the correct ratio and quantity for combustion in an internal-combustion engine, adjusting that mixture as engine load and speed change. In practical terms, it atomizes gasoline into the incoming airstream and regulates airflow to control power and responsiveness—an approach still common on small engines and older vehicles, even as most modern cars use electronic fuel injection.

How a Carburetor Does Its Job

A carburetor leverages the pressure drop created by a venturi (a narrowed passage in the air intake) to draw fuel from a reservoir and blend it with incoming air. As the throttle opens, more air flows through the venturi, pulling more fuel and increasing engine power. Supporting circuits and components stabilize this process across different operating conditions, from cold starts to hard acceleration.

Key components and their roles

The following list outlines the core parts that enable a carburetor to mix and meter fuel and air effectively.

• Venturi: Narrows airflow to create a pressure drop that draws fuel into the airstream (Bernoulli effect).
• Float bowl and needle valve: Maintain a constant fuel level so delivery remains consistent.
• Main jet(s): Meter fuel flow at cruising and higher throttle openings.
• Idle circuit: Supplies a stable, finely metered mixture when the throttle is nearly closed.
• Throttle plate (butterfly): Controls airflow and, by extension, engine power and speed.
• Choke: Temporarily enriches the mixture for cold starting.
• Accelerator pump: Adds a quick shot of fuel to prevent hesitation when the throttle is snapped open.
• Mixture screws: Allow fine-tuning of idle and low-speed air–fuel balance.

Together, these elements ensure the carburetor can produce a combustible, well-atomized mixture and adjust fuel delivery with changes in throttle position and engine demand.

Why the Air–Fuel Ratio Matters

Engines need a specific balance of air and fuel to run efficiently and cleanly. For gasoline, the stoichiometric ratio is about 14.7 parts air to 1 part fuel by mass, though richer mixtures (around 12.5:1) often produce peak power and leaner mixtures (up to ~16–18:1) can improve economy under light load. Carburetors approximate these targets mechanically, but changes in temperature, altitude, and load can shift the ideal setting.

Operating scenarios that change mixture needs

The following scenarios illustrate when and why the carburetor alters fuel delivery and airflow.

1. Cold start: Extra fuel is needed for easier ignition, hence the choke enriches the mixture.
2. Idle: Minimal airflow requires a dedicated idle circuit for smooth, stable running.
3. Acceleration: A quick squirt from the accelerator pump prevents a lean stumble.
4. Cruise: The main jet meters a near-stoichiometric mixture for efficiency and drivability.
5. Wide-open throttle: A richer blend improves power and helps manage combustion temperatures.
6. High altitude or heat: Thinner, warmer air demands less fuel; uncorrected, the mixture runs rich.

Because these conditions vary constantly, the carburetor’s circuits balance fuel delivery across a wide range—but with less precision than modern electronic systems.

Carburetor vs. Fuel Injection

While carburetors remain common in small engines, classic cars, and some motorcycles, fuel injection dominates modern automobiles because it can meter fuel far more precisely using sensors and electronic control. Injection adapts quickly to altitude and temperature changes, improves cold starts, enhances emissions control, and often boosts both power and efficiency. Carburetors, however, are mechanically simple, relatively inexpensive, and easy to service and tune without specialized equipment.

Summary

A carburetor’s primary function is to mix and meter air and fuel into a combustible, well-atomized mixture tailored to engine demand. It uses a venturi-driven pressure drop, jets, and control circuits to adjust that mixture for starting, idling, cruising, and acceleration. Though largely replaced by fuel injection in modern cars, carburetors remain effective and widely used in applications where mechanical simplicity and ease of maintenance are priorities.

Why did they stop using carburetors?

Fuel injection systems eventually replaced carburetors because they could be better controlled, which provided more efficient fuel use, lesser pollution, and lesser fuel consumption as well. Power and performance were the main reasons why fuel injection systems began to replace the carburetor starting in 1970.

What is the function of the simple carburetor?

A simple carburettor is a device that mixes air and fuel to create a combustible mixture for a gasoline engine. It consists of a float chamber, main fuel jet, venturi, jet tube, and throttle valve. The float chamber contains a float, which helps to maintain a constant level of fuel.

What is the main function of the carburetor?

A carburetor’s function is to precisely mix fuel with air in the correct ratio, vaporizing the fuel to create a combustible mixture before it enters the engine’s combustion chamber. It works by using Bernoulli’s principle, where air flowing through a narrowed passage (the venturi) creates a low-pressure area that sucks in fuel. A throttle valve then controls the amount of this air-fuel mixture that goes into the engine, thereby regulating engine speed and power.
 
This video provides a good overview of how a carburetor works, including the role of the venturi and throttle valve: 52sDonutYouTube · Jul 25, 2018
Key Components & Principles

• Venturi: Opens in new tabA constricted section in the carburetor that speeds up airflow and creates a low-pressure zone, which draws fuel from the fuel reservoir. 
• Fuel Delivery: Opens in new tabA float-controlled fuel reservoir maintains a constant fuel level and a capillary tube delivers fuel to the venturi, where it’s atomized into fine droplets. 
• Throttle: Opens in new tabA butterfly valve that opens or closes to control the amount of air (and thus the air-fuel mixture) entering the engine, which directly affects the vehicle’s speed. 
• Choke: Opens in new tabA valve that restricts airflow during a cold start, creating a richer fuel-air mixture (more fuel, less air) to compensate for poor vaporization and help the engine start. 
• Air-Fuel Ratio: Opens in new tabFor optimal combustion, the ideal ratio is around 14.7 parts air to 1 part fuel by weight. A lean mixture has too much air, while a rich mixture has too much fuel. 

How it Works

1. Air Intake: Air is drawn into the carburetor. 
2. Pressure Drop: As the air passes through the venturi, its speed increases, and its pressure decreases. 
3. Fuel Draw: The lower pressure in the venturi sucks fuel from the float bowl through a small jet. 
4. Mixture Creation: The fuel atomizes and mixes with the incoming air. 
5. Engine Input: The resulting air-fuel mixture enters the engine. 
6. Throttle Control: The driver presses the gas pedal to open the throttle, allowing more air-fuel mixture into the engine and increasing power and speed. 

You can watch this video to see a detailed demonstration of how the throttle and choke work to control the air-fuel mixture: 1mSmarterEveryDayYouTube · Jun 30, 2021
Modern vs. Carbureted Engines
Most modern vehicles use more efficient and precise fuel injection systems instead of carburetors. However, carburetors are still used in some smaller engines, such as those found in lawnmowers, motorcycles, and certain off-road vehicles.

Does a carburetor add horsepower?

Carburetors can make more peak power than electronic fuel injection (EFI) in specific, high-performance applications, primarily due to a phenomenon called charge cooling. Introducing fuel earlier in the intake path cools the incoming air, which increases its density and can lead to greater power, especially up to a certain RPM range. However, carburetors are less efficient and precise than EFI, which can provide better overall performance, fuel economy, and adaptability to varying conditions. 
How Carburetors Can Increase Power

• Charge Cooling: The evaporation of fuel in the intake manifold cools the intake air. Cooler, denser air allows more oxygen into the cylinders, leading to a more powerful combustion event and more horsepower. 
• Rich Air-Fuel Ratios: For maximum power, engines often run with a slightly richer air-fuel mixture than what is optimal for efficiency. Carburetors can be tuned to achieve these richer mixtures for peak power. 
• Tuning for Specific Conditions: A properly tuned carburetor can be set to deliver more fuel than a standard EFI system, resulting in a power advantage. 

Why Fuel Injection Is Generally Superior

• Precise Fuel Delivery: EFI systems use sensors to constantly adjust the air-fuel mixture for varying engine conditions, such as temperature and altitude. 
• Greater Efficiency: EFI’s precise control leads to more efficient fuel combustion, resulting in better fuel economy and lower emissions. 
• Smoother Power Delivery: While carburetors can provide excellent peak power, EFI typically offers a smoother, broader powerband across the entire RPM range. 
• Improved Reliability: EFI eliminates many mechanical components and the need for constant manual tuning, leading to better reliability and easier starting. 

Conclusion
While carburetors can be an excellent choice for certain performance builds focused on maximum power in specific RPMs, modern EFI systems generally offer superior overall performance, efficiency, and adaptability for most applications.