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You may not know, but there are different types of carburetors used in different vehicles. These carburetor types are designed to function uniquely based on the way a car’s engine is configured to run. The generally known types of carburetors are Updraught, Downdraught, and Side Draught.
Carburetors are used in – pretty – old vehicles; newer vehicles use injectors. The carburetors are used in ICE vehicles to help air and fuel mixture for combustion to carry on successfully – and make the engine run smoothly.
While carburetors are no longer common in modern vehicles, they are still used in motorbikes and smaller engines. This article details the common carburetor types you should know and how they function.
What Does a Carburetor Do?
“Carburetor” is a device used to complement the design of engines. It is usually installed around the inlet manifold to assist combustion.
The carburetor provides a passageway for air – from the atmosphere – to enter the inlet valve(s) and then to the combustion chamber. You’d find only one carburetor in most engines, but some high-performance vehicles use multiple carburetors.
Basically, the carburetor controls the amount of air that goes into the combustion chamber to ensure appropriate air and fuel mixture. Some people shortened the name to carb or carby, so when you hear auto enthusiasts or mechanics mention “carb” or “carby,” they are most likely referring to carburetors.
A typical carburetor consists of the following: throttle valve, strainer, venturi, metering system, idling system, float chamber, mixing chamber, idle and transfer port, and choke valve.
Components of a Carburetor Explained
| Component | Function |
| Throttle Valve | Regulates the supply of a steamy fluid or gas and air into the engine. It is operated automatically by a governor, a handwheel, or a lever. |
| Strainer | Removes dust/particles from the fuel – using a fine wire mesh – before sending it to the float chamber. If these particles are not filtered out, they could clog the nozzle. |
| Venturi | The narrowed neck air passageway that speeds up airflow and reduces pressure drops. The venture has a small vacuum inside; the fuel jet opens into the venturi. |
| Metering System | Consists of a metering orifice and fuel discharge nozzle for controlling fuel flow into the nozzle – ensuring a correct air-fuel mix. |
| Idling System | Provides a direct passageway from the float chamber to the venturi tube. Also ensures a rich air-fuel mixture during idling or low speeds when the throttle is about 15% possible. |
| Float Chamber | Automatically regulates the supply of fuel into the engine. It consists of a float valve that regulates the fuel level in the chamber. This is the fuel storage tank in carburetor engines. |
| Mixing Chamber | As the name implies, this is the place where air and fuel mix, and are then sent to the engine’s cylinders. |
| Idle And Transfer Port | Comes as an additional channel to the main nozzle in the venturi to ensure seamless fuel delivery into the engine cylinders. |
| Choke Valve | Controls the amount of air in the mixing chamber to ensure an appropriate air-fuel mixture. |
Types of Carburetors
Carburetors are categorized based on different factors: float chamber design, airflow direction, number of units, type of metering system, venturi type, and so on.
Hereunder, we’d explain the most common classifications.
1. Based on Airflow Direction
There are three types of carburetors based on airflow direction – upward, downward, and side/horizontal.
– Updraught Carburetor
Updraught carburetors are carburetors that allow air to enter from the bottom side and then send the air upwards – against gravity.
This type of carburetor lift sprayed fuel droplets by air friction and may not be able to ensure rapid speed air-fuel mixture when driving at top speeds. Well, updraught carburetors are almost obsolete; you’d almost not find them in any engine anymore.
– Downdraught carburetor:
In contrast to updraught carburetors, downdraught ones allow air penetration from the topside, and the air travels downward with the help of gravity; hence, some people call it a gravity-assisted carburetor. This type of carburetor is usually installed atop the intake manifolds, and they allow the appropriate flow of air-fuel mixture at any speed.
– Horizontal or side draught carburetor:
This type of carburetor allows air to come in from one end, and then mixing takes place in the chamber before being sent to the engine’s cylinders for combustion. Side draught carburetors have reduced flow resistance due to the absence of the right angle mechanism in the intake area.
2. Based on Float Chamber Design
There are two main types of carburetors based on this classification – Eccentric and Concentric.
– Eccentric
This type of carburetor has its float chambers installed beside the venturi tube. However, eccentric float chamber-type carburetors do not provide accurate air-fuel mixtures at high speeds – they are more like updraught carburetors.
– Concentric
Concentric float chamber carburetors have their float chambers installed somewhere around the venturi tube – not necessarily by the side as with “eccentric” types.
This type of carburetor is more efficient than eccentric types, as they provide a more accurate correct air-fuel mixture to the engine at any speed.
3. Based on Units
Units here mean the number of barrels or venturis used in the carburetor. There are typically three classifications in this category.
– One-Barrel
This type of carburetor has only one single outlet that acts as the passageway for all the systems – carburetor components – to feed to the intake manifold. It is also called a single-venturi carburetor. You’d find this carburetor in four-cylinder and six-cylinder engines.
– Two-Barrel
Two-barrel carburetors have dual barrels and throttles that operate together – as single-barrel carburetors. The throttle plates are installed on the same shaft, and the two barrels share the same float, power system, choke, and acceleration pump.
There’s another design of two-barrel carburetors where the throttle plates operate independently – referred to as two-stage dual-barrel carburetors.
– Four-Barrel
Comprises two units of dual barrels in one body; dual independent primary barrels and dual independent secondary barrels.
The primary barrels function as single-stage two-barrel at low-to-moderate engine speeds and loads, and the secondary barrels open at about half to three-quarter throttle to provide the increased fuel and airflow required for high speeds.
The primary and secondary barrels have their own accelerator pump and power systems. You’d mostly find these carburetors in V8 engines.
4. Based on Power System
There are two main types of carburetors based on this category: manually operated and vacuum controlled.
– Manually Operated
In manually operated carburets, the power jets are operated by a mechanical linkage to the throttle shaft. The jets are controlled by the engine’s speed – the vacuum passages produce a high vacuum that pushes the piston down against the spring to keep the jet closed.
– Vacuum Controlled
This type of carburetor is called a step-up system, where the intake manifold vacuum falls off to push the piston up and raises the step-up rod out of the jet for more extra fuel to flow in from the float chamber.
Summary
Carburetors are no longer commonly used in modern vehicles, but it’s important you know these types of carburetors if you’ve got engines that use the system. This article explains various types of car carburetors based on different classification factors.
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