Carburetor

A carburetor (american spelling), carburettor, carburetter (commonwealth spelling) or Karburator  (danish spelling) is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom.

Word origin
The word carburetor comes from the French carbure meaning "carbide". Carburer means to combine with carbon. In fuel chemistry, the term has the more specific meaning of increasing the carbon (and therefore energy) content of a fuel by mixing it with a volatile hydrocarbon.

Principles
The carburetor works on Bernoullis principle: the faster air moves, the lower its static pressure, and the higher its dynamic pressure. The throttle (accelerator) linkage does not directly control the flow of liquid fuel. Instead, it actuates carburetor mechanisms which meter the flow of air being pulled into the engine. The speed of this flow, and therefore its pressure, determines the amount of fuel drawn into the airstream.

Basics
A carburetor basically consists of an open pipe through which the air passes into the inlet manifold of the engine. The pipe is in the form of a venturi: it narrows in section and then widens again, causing the airflow to increase in speed in the narrowest part. Below the venturi is a butterfly valve called the throttle valve — a rotating disc that can be turned end-on to the airflow, so as to hardly restrict the flow at all, or can be rotated so that it (almost) completely blocks the flow of air. This valve controls the flow of air through the carburetor throat and thus the quantity of air/fuel mixture the system will deliver, thereby regulating engine power and speed. The throttle is connected, usually through a cable or a mechanical linkage of rods and joints or rarely by pneumatic link, to the accelerator pedal on a car or the equivalent control on other vehicles or equipment.

Fuel is introduced into the air stream through small holes at the narrowest part of the venturi and at other places where pressure will be lowered when not running on full throttle. Fuel flow is adjusted by means of precisely calibrated orifices, referred to as jets, in the fuel path.

Float chamber
To ensure a ready mixture, the carburetor has a "float chamber" (or "bowl") that contains a quantity of fuel at near-atmospheric pressure, ready for use. This reservoir is constantly replenished with fuel supplied by a fuel pump. The correct fuel level in the bowl is maintained by means of a float controlling an inlet valve, in a manner very similar to that employed in a cistern (e.g. a toilet tank). As fuel is used up, the float drops, opening the inlet valve and admitting fuel. As the fuel level rises, the float rises and closes the inlet valve. The level of fuel maintained in the float bowl can usually be adjusted, whether by a setscrew or by something crude such as bending the arm to which the float is connected. This is usually a critical adjustment, and the proper adjustment is indicated by lines inscribed into a window on the float bowl, or a measurement of how far the float hangs below the top of the carburetor when disassembled, or similar.

Carburetor adjustment
Too much fuel in the fuel-air mixture is referred to as too rich, and not enough fuel is too lean. The mixture is normally adjusted by one or more needle valves on an automotive carburetor, or a pilot-operated lever on piston-engined aircraft (since mixture is air density (altitude) dependent). The ([Stoichiometry|stoichiometric) air to gasoline ratio is 14.7:1, meaning that for each weight unit of gasoline, 14.7 units of air will be consumed. Stoichiometric mixture are different for various fuels other than gasoline.

Ways to check carburetor mixture adjustment include: measuring the carbon monoxide, hydrocarbon, and oxygen content of the exhaust using a gas analyzer, or directly viewing the colour of the flame in the combustion chamber through a special glass-bodied spark plug sold under the name "Colortune"; the flame colour of stoichiometric burning is described as a "bunsen blue", turning to yellow if the mixture is rich and whitish-blue if too lean.

The mixture can also be judged by removing and Spark_plug. Black, dry, sooty plugs indicate a mixture too rich; White to light gray plugs indicate a lean mixture. A proper mixture is indicated by brownish-gray plugs.

In the 1980s, many American-market vehicles used special "feedback" carburetors that could change the base mixture in response to signals from an exhaust gas oxygen sensor. These were mainly used because they were less expensive than fuel injection systems; they worked well enough to meet 1980s emissions requirements and were based on existing carburetor designs. Eventually, however, falling hardware prices and tighter emissions standards caused fuel injection to supplant carburetors in new-vehicle production.

Where multiple carburetors are used the mechanical linkage of their throttles must be synchronized for smooth engine running.

Manufacturers

 * Argelite, producer of Holley and Magneti Marelli carburetors for the Argentinian market
 * Autolite, a division of the Ford Motor Company from 1967-1973.
 * Ball & Ball, US manufacturer, eventually part of Carter
 * Bendix Stromberg and Bendix Technico carburetors used on aircraft and vehicles made by Chrysler, IHC, Ford, GM, AMC, and Studebaker
 * Bing Carburetor, used on motorcycles, mopeds, aircraft, boats.
 * Carter carburetor, used on numerous makes of vehicles, including those made by Chrysler, IHC, Ford, GM, AMC, and Studebaker, as well as on industrial and agricultural equipment and small engines.
 * Claudel-Hobson, UK
 * Dell'Orto carburetors from Italy, used on cars and motorcycles
 * Demon Carburetors
 * Edelbrock performance carburetors
 * Hitachi carburetors, found on Japanese automobiles
 * Holley, with usage as broad as Carter and Weber.
 * Keihin, a keiretsu group company affiliated with Honda
 * Lectron Fuel Sysytems carburetors
 * Marvel Schebler carburetor, used for aircraft, tractors, ...
 * Mikuni, common on Japanese motorcycles, especially in the 1980s. Mikuni also made Automotive Racing Carburetors for Japanese, British and European cars. Original equipment carburetors supplied on Mitsubishi engines.
 * Motec Engineering - high-performance updraft carburetors
 * Pierburg carburetor, in Saab, Volvo, VW and Audi
 * Rochester Products Division, USA (A General Motors subsidiary; also sold Weber/Magneti Marelli carburetors under license)
 * Solex carburetor
 * SU carburetor widely used on British Commonwealth and European-designed vehicles
 * AMAL Carburetter Company, supplier to the British motorcycle industry
 * UCAL FUEL SYSTEMS - Carburettors
 * Villiers UK Motorcycle and small engines
 * Walbro and Tillotson carburetors for small engines
 * Weber carburetor, Italian, now made in Spain, owned by Magneti Marelli
 * Zenith UK — Also produced the Zenith-Stromberg Carburetors

General information

 * Know Your Carburetor. Popular Mechanics, Jul 1953.
 * American Technical Society. (1921). Automobile engineering; A general reference work. Chicago: American technical society.
 * Lind, W. L. (1920). Internal-combustion engines; Their principles and applications to automobile, aircraft, and marine purposes. Boston: Ginn.
 * Hutton, F. R. (1908). The gas-engine. A treatise on the internal-combustion engine using gas, gasoline, kerosene, alcohol, or other hydrocarbon as source of energy. New York: Wiley.

Patents
American
 * U.S. Patent 610,040 — Carburetor —Henry Ford
 * U.S. Patent 1,750,354 —Carburetor — Charles Nelson Pogue
 * U.S. Patent 1,938,497 —Carburetor — Charles Nelson Pogue
 * U.S. Patent 1,997,497 —Carburetor — Charles Nelson Pogue
 * U.S. Patent 2,026,798 —Carburetor — Charles Nelson Pogue
 * U.S. Patent 2,214,273 —Carburetor — J. R. Fish
 * U.S. Patent 2,982,528 —Vapor fuel system — Robert S. Shelton
 * U.S. Patent 4,177,779 —Fuel economy system for an internal combustion engine — Thomas H. W.

Other
 * G.B. Рatent 11119 — Mixing chamber — Donát Bánki