Carburetor

The Carburetor, also known as carb or carbie for short, is a device that mixes air and fuel for an internal combustion (IC) engine. Carburetor are still found in small engines and some older or specialized automobiles such as those designed for stock car racing. However, fuel injection (FI), first introduced in late 1950s and first successfully commercialized in the early 1970s, is now the preferred method of automotive fuel delivery. The majority of motorcycles still are carbureted due to lower weight and cost, but as of 2005 many new models are now being introduced with fuel injection.

Most carbureted engines have single carburetor, though some engines use multiple carburetors. Older engines used updraft carburetors, where the air enters from below the carburetor and exits through the top. This had the advantage of never “Flooding” the engine, as any liquid fuel droplets would fall out of the carburetor instead of into the intake manifold; it also lent itself to use of an oil bath air cleaner, where a pool of oil below the mesh element below the carburetor is sucked up into the mesh and the air is drawn through the oil covered mesh; this was an effective system in a time when paper air filters did not exist. Small propeller driven flat aircraft engines still use the updraft carburetor design.

Functions of a Carburetor:

The major function which a carburetor is required to perform are:

·        To keep a small reserve of a fuel at a constant head,

·        To vaporize the fuel to prepare a homogeneous air fuel mixture,

·        To supply correct amount of the air fuel mixture the correct strength under all conditions of load and speed of the engine.

Principle of Carburetor:

The carburetor works on the Bernoulli’s principle: the fact that moving air has lower pressure than still air, and that the faster the movement of the air, the lower the pressure. The throttle or accelerator does not control the flow of liquid fuel. Instead, it controls the amount of air that flows through the carburetor. Faster flows of air and more air entering the carburetor draws more fuel into the carburetor due to the partial vacuum that s created.

Adjustments in Carburetor:

The procedure to make various adjustments differs in case of individual carburetor models. However, the common adjustments and their procedures may be outlined as given below:

1.      Idle adjustment

There is an idle adjustment screw provided in the carburetor. Screwing in the same decreases the idle port area and hence decreases the engine speed. The screw is adjusted till the engine runs smoothly at required speed. Generally, this is done by screwing in completely and then opening back by one or two turns. Another method for idle adjustment, which is precise, involves attaching a vacuum gage to the intake manifold and adjusting the idle screw till maximum vacuum is obtained on the gage.

2.      Throttle adjustment

On releasing the accelerator pedal throttle valve should be completely closed, while on pressing the pedal fully, it should be in full open position. This may be checked and if not found correct, the linkage may be adjusted, as provided for in the manufacturer’s manual.

3.      Other adjustments

Apart from the idle and throttle adjustments, the other adjustments which are provided in some carburetors are for accelerating pump, metering rod, floats, etc. They may be performed as laid down in the manual.