What is Carburetor?- Definition, Types & How it works

One popular term for the carburetor is the ‘Heart’ of the automobile. It is not possible to expect the engine to perform properly, supply the proper horsepower or operate smoothly, if the ‘heart’ is not fulfilling its job.

What is a carburetor?

Carburetors – sometimes spelled carburettor – are devices that supply a spark-ignition engine with a mixture of air and fuel.

Components of carburetors typically include a chamber for storage of liquid fuel, a choke, an idling (or slow-running) jet, a main jet, a venturi-shaped air-flow obstruction, and an accelerator pump.

Carburetors add gas to air to make a mixture that is just right to burn in engine cylinders. Carburetors have been replaced for more efficient delivery of fuel through fuel injections for modern car cylinders. Fuel injectors typically use less fuel and make less pollution.

However, engines in older cars and motorcycles, and the compact engines in lawnmowers, and chainsaws have carburetors.

The design of gasoline engines is to take in precisely the right amount of air so that whether the engine is starting from the cold or running hot at its top speed, it burns the right amount of fuel.

The job of getting the proper air-fuel mixture is done by an ingenious mechanical device called a carburetor, a tube allowing air and fuel to enter the engine’s through valves, mixing them together in order to meet a range of different driving conditions.

You might think that “carburetor” is a weird term, but it derives from the verb “carburet,” a chemical term describing the act of enriching a gas by combining it with carbon or with hydrocarbon.

So a carburetor is technically a device that saturates air (the gas) with fuel (the hydrocarbon).

Who invented the carburetor?

The first carburetor was invented by Samuel Morey in 1826. The first person to patent a carburetor for use in a petroleum engine was Siegfried Marcus. He was awarded U.S. Patent #128541 on July 6, 1872 for a “device for mixing fuel with air.”

The diagram below is a very simplified version of Karl Benz original carburetor from his patent from 1888. Raw fuel from the tank enters what he called the generator, underneath where the raw fuel evaporates.

The fuel vapor passes up through the gray pipe to where it meets air flowing downwards, entering from our atmosphere through perforations at the top of the gray pipe.

The air and fuel mix in this chamber and enters into a cylinder through a valve, burns down there creating power.

Carburetor Diagram

Parts of Carburetor

The following are the Parts of the Carburetor:

• Throttle Valve
• Strainer
• Venturi
• Metering system
• Idling system
• Float Chamber
• Mixing Chamber
• Idle and Transfer port
• Choke Valve

• Throttle Valve: A valve used to control the flow of a fluid such as steam, gas, and air, to an engine, and can be operated by a handwheel, lever, or automatically by a governor.
• Strainer: A pre-filtering device for the fuel flow to the float chamber, constructed of fine wire mesh to filter the fuel and remove everything in it. Particles left are capable of blocking the nozzle.
• Venturi: The air passes through a narrowed neck of the carburetor, the venturi, where it speeds up flow. As air speeds, it drops in pressure (slight vacuum). The fuel jet opens into the venturi and is sucked through the jet, into the air stream, by the partial vacuum.
• Metering system: The fuel discharge nozzle is located in the carburetor barrel so that its open end is located in the throat (narrowest part) of the venturi. It is this difference in pressure, or metering force, that allows the fuel to flow from the discharge nozzle.
• Idling system: The idling system gives the air fuel charge at speeds below approximately 800 rpm/20 mph. When the engine is idling the throttle is almost completely closed. All the engine needs at idle speed is enough air, which also restricts air flow through the air horn to create enough of a vacuum in the venturi.
• Float Chamber: Generally, a float chamber is a device that automatically regulates the supply of water to a system. In this case a float chamber is most commonly found in the carburetor of an internal combustion engine. It meters the fuel supply to the engine automatically.
• Mixing Chamber: This is where the air and fuel are mixed and pushed to the engine cylinder.
• Idle and Transfer Port: In addition to the main nozzle in the venturi of the carburetor, there are two other nozzles, or ports, that add fuel to the engine cylinder.
• Choke Valve: A choke valve is sometimes fitted to internal combustion engines in the carburetor. Its purpose is to close off air so that the fuel air mixture is richer while starting engine.

How Does A Carburetor work?

Carburetors use the vacuum force produced by the engine to draw in air and fuel to the cylinders. The throttle can open and close which allows for more or less air to enter the engine.

This air moves through a constricted part of the carburetor called a venturi and it creates the vacuum force necessary to continue running the engine. Carburetors are very different in instruments and operation.

The simplest carburetor is basically a tall vertical air pipe above the engine cylinders with one horizontal fuel pipe connecting to the side. As air flows down the vertical pipe, it has to pass through a kink in the middle of the pipe.

This makes the air speed up and causes a drop in air pressure. Case in point, a kinked section in a pipe is a venturi. So, with the air pressure dropping, this creates a sucking effect that draws air in through the fuel pipe from the side.

When a fluid moves into a smaller confined space, its speed increases and pressures drop. So, if you look at the street on windy day, the wind makes a whistling sound as it passes between buildings. Or, when canal boats that are drifting side by side, are drawing close together.

This is a demonstration of a conservation of energy. If the pressure did not drop, the fluid would get any extra energy as it moves into the smaller space and would violate one of the most fundamental laws of physics, that fluid cannot gain extra energy.

Let’s observe how a Carburetor works during normal operation:

• Air flows into the top of the carburetor from the car’s air intake and passes through an air filter to remove debris.
• When the engine is first started, the choke can be set so it blocks nearly 100% of the top air space, allowing less air so it increases the fuel content of the mixture entering the cylinders.
• In the center of the tube, we use a venturi to3 focus or constrain the air flow into a narrow pipe. This speeds up and is dropping the air pressure.
• Because of the drop in air pressure there is suction from the fuel pipe, creating fuel flow.
• The throttle is a valve which opens or closes the pipe by swiveling. If the throttle is opened then mores air can be drawn in to the cylinder together with fuel which makes more power out of the engine so the car can go faster.
• The air and fuel mixture flows down into the cylinders.
• The fuel is coming from a mini-fuel tank called a float-feed chamber.
• As fuel level drops, float drops and this opens a valve at the top.
• As the valve opens, it allows more fuel to flow into the float-feed chamber from the main gas tank. This causes the float to rise and close the valves again.

Types of Carburetor

There are three types of carburetors:

• Up-draft carburetors
• Horizontal type carburetors
• Down-draft type carburetors

#1. Updraft type carburetors.

Despite their complexity and the increasing use of electronic fuel injection, updraft carburetors were the most common type of carburetors, which called for an air-fuel mixture that passed through the carburetor from below upwards.

According to Edward Abdo in Power Equipment Engine Technology, the air in an Updraft carburetor comes up into the venturi, making this the original type of carburetor to be used.

There are also downdraft and side-draft carburetors, which do not typically use a drip collector for the drain and disposal of fuel if the carburetor nutrient goes below minimum weight.

#2. Down-draft Carburetors.

This is a carburetor that can use lower air velocities, will have larger passages as it takes gravity feed to the cylinder head.

Downdraft carburetors can deliver large volumes of fuel quickly for high speeds and high levels of power.

In a downdraft carburetor, air enters at the top of the mixing chamber and fuel enters from the bottom. The mixture produces air-fuel mixture and draws it into the venturi through the outlet tube to lessen airflow pressure.

#3. Horizontal Type Carburetors.

This type of carburetor is used when we have the space constraint of assembly, like the horizontal or side draught carburetor, which, as it suggests, has the jet tube being in a horizontal direction.

This type of carburetor would have the advantage of reducing the resistance of the flow of the air-fuel mix, as there is no right-angle turned mechanisms included in the mix in the intake area to enter the carburetor and mix.

The working principle of this type of carburetor is straightforward. The carburetor would remain horizontal as the air enters at one end of the carburetor, at a lower part of the carburetor. This air would mix with the fuel at the same time, creating the air-fuel mixture to go into the engine cylinder to complete combustion.

How To Clean A Carburetor?

Before you clean the carburetor, you should check your Owner’s Manual. Always follow the full detail of the manufacturer when cleaning and maintaining equipment and always clean the carburetor when cool to the touch.

#1. Dilute cleaner.

In a large container mix dilute cleaner When you select cleaner, never select corrosive cleaners that can damage or degrade the plastic and rubber elements of the carburetor.

Do not use vinegar as the acetic acid promotes rust on the metal. Do not use bleach, either; sodium hypochlorite (bleach) will rust out metals like aluminum or steel, and degrade rubberized seals.

#2. Clear air filter.

Inspect the air filter to be sure that the air that will flow into the carburetor is clean, and that there are no filter blockages, that, when allowed to operate, will produce black smoke from the exhaust.

Shut-off fuel, and disconnect the spark plug wire, if equipped. Remove the housing, and the wing nut that attaches the air filter, removing any outer element. Use compressed air in a can to blow-off debris.

#3. Remove the carburetor.

Remove any plate or shield covering the carburetor. Then remove any linkage or hoses using pliers or a screwdriver if necessary. Also, remove any clamp or cover that attaches the carburetor. Remove the hose clamp attached to the fuel line.

Finally remove the carburetor and use compressed air to blow-off excess dirt on the outside casing (Note: If you’re have never done this, you should seek help from professional before attempting to clean the carburetor.

#4. Remove the carburetor float.

Loosen and/or remove the bolt that holds the carburetor float (a bowl-shaped container for gas) in place, while dumpster diving to ensure that any remaining gas stays inside the float, and always dispose of according to regulations. This is usual place for varnish build-up on carburetors.

Remove the pin that the float pivots on, and keep to the side in a safe place, then pull the float castle straight out of the casing.

#5. Remove any other removable items.

Be sure to note where the other carburetor items come from in order to swap them around for (a) cleaning.

#6. Soak and scrub components.

Submerge the carburetor float and other components in the large container of dilute cleaning solution, and let the components soak for 10 minutes.

Now take a brass brush and scrub everything that’s metal, and a stiff nylon brush to scrub the plastic pieces. Remember to clean the tiny vents. Also throw the little parts into the cleaning solution as well.

#7. Rinse and dry.

Rinse all carburetor components in a bucket of clean water, and allow components to completely air dry. For any small holes and vents, use compressed air to blow off any excess water.

#8. Reassemble and replace.

Carefully reassemble the carburetors, and place the to the engine. Re-link hoses, clamps, and wires.

Functions of carburetors:

The primary role of a carburetor is to:

• Combines air and gasoline and supplies a good combustion mixture on low delivery requirements
• Control engine speed
• Control and regulate the air-fuel ratio
• Increase the amount of mixture or decrease it depending on how many changes to engine speed and load.
• For the float chamber to always keep a certain head of fuel.
• Vaporizes the fuel and mixes it to air into a homogenous air-fuel mixture
• Delivers the appropriate amount of air-fuel mixture at the right strength under all conditions of engine load and engine speed.

Advantages of the carburetor:

• Carburetor parts are inexpensive than fuel injectors.
• From a carburetor, you receive more air, and fuel mixture
• In road testing, carburetors perform with more power and precision than fuel injectors.
• Carburetors are unrestricted to the amount of gas being pumped from the fuel tank, which means cylinders could pull more fuel through the carburetor that leads to a denser mixture in the chamber and more power.

Disadvantages of the carburetor:

• The mixture supplied by a carburetor at very low speeds is so weak that it will not ignite properly. For its enrichment, at such conditions, a special arrangement in the carburetor is required.
• The working of a carburetor will respond to changes in the atmospheric pressure.
• More fuels will be consumed because carburetors are heavier than fuel injectors.
• More air emissions will be released by the carburetor than the fuel injectors.
• Carburetors are used up more because their maintenance costs are higher than fuel injection systems.

Applications of Carburetor:

• Spark-Ignition Engine.
• Carburetor used to regulate the speed of the vehicles.
• The carburetor converts the main fuel petrol into fine droplets and mixes together with air to burn in smoothly and properly without any trouble.

FAQs.