combustion engine. The main function of a carburetor is to mix
the fuel and air and feed it into the vehicle's combustion chambers where its ignited
and used to thrust the pistons downward inside the engine block. This force against
the pistons is what creates power and causes a car to accelerate. The basic physics
behind the function of a carburetor is called the "Bernoulli principle" the venturi
effect. The Bernoulli principle states that speed of the air is inversely proportional
to the pressure. The throttle plate or butterfly of the carburetor manages the amount
of air flow that is delivered to the engine.
The velocity of the air flow and the subsequent pressure, gauges
the quantity of emulsified fuel that is fed into the air stream. Carburetors use
tubes called venturies to achieve this effect. Below the venturi there is a valve
called a throttle plate which can be open and closed by the gas pedal. This controls
the engine speed by restricting the air flow to the engine and subsequently, the
amount of air & fuel mixture that is delivered into the engine. When the gas pedal
is depressed, fuel is drawn into the air stream via the venturies and the engine
The main problem with a carburetor is dirty fuel, this can cause the carburetor
to malfunction. To check a carburetor air/fuel mixture a gas analyzer is needed.
This will measure the carbon monoxide, hydrocarbon and oxygen content of the exhaust.
During a normal smog inspection the fuel/air mixture is tested and a report is generated.
When a tune up is performed the spark plug insulator can indicate a lean or rich
mixture. Brownish grey is the desired color and confirms proper mixture. Black and
sooty means the mixture is too rich while white to light grey confirms a lean mixture.
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- Accelerator pump (used to inject fuel into the engine just as the throttle
is opened. Accelerator pump also primes the engine at cold starts.)
- Idle circuit (used to supply a small amount of fuel to the engine at idle
- Fuel jets (used to meter the raw fuel allowed into the venturies which is
then mixed with air.)
- Throttle plate (used to meter the amount of fuel-air mixture allowed into
- Choke (used to increase the amount of fuel drawn into the engine when cold
only. A cold engine needs a rich mixture to run properly. The choke also holds
the throttle plate open slightly to increase the idle speed to prevent stalling.)
- Fuel level float (used to maintain the proper fuel level inside the carburetor.)
- Fuel filter (used to filter fuel before it enters the carburetor.)
Changing the air filter and fuel filter will keep dirt/debris from entering the
internal workings of the carburetor. Air and fuel filters should be changed at regular
intervals. Visit -
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