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How Does it Work /
Carburetor
How a Carburetor Works
A carburetor is an essential part of older model internal combustion engine vehicles.
The main function of a carburetor is to mix the fuel and air and feed it into the
vehicle's engine where it is 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 and maintain motion. The basic physics behind the function of
a carburetor is called the Bernoulli Principle and the Venturi effect. The Bernoulli
Principle states that speed of the air is inversely proportional to the pressure.
It is the throttle plate or butterfly of the carburetor that manages air flow that
is delivered to the engine.
Carburetor - (appearance may vary)
The velocity of the flow and the subsequent pressure, gauges the quantity of
fuel feed into the air stream. The Venturi effect is an example of the Bernoulli
principle. Fluid velocity must increase through the constriction in a tube. The
kinetic energy is created by the drop in pressure. Carburetors use tubes called
venturis to achieve this effect.
Below the venturi there is a valve called a throttle plate which is can be open
and closed by the the throttle peddle. This controls the engine speed by restricting
the air flow to the engine and subsequently the amount of air & fuel mixture that
is delivered.
Mathematical Equation - (ρ/2)(v22 - v12)
When the gas pedal is depressed, fuel is drawn into the air stream. These tiny
holes are on the smallest section of venturi and called jets. When the throttle
is opened the vacuum in the intake manifold is decreased. The velocity of air increases,
the low pressure raises the air speed to draw additional fuel into the air stream
through the nozzle located at the center area of venturi.
Other parts of the carburetor are an accelerator pump and choke assemblies. The
accelerator pump forces a small quantity of gasoline through the jet when the throttle
is first opened off of idle mode. This helps a natural stumble during the need for
fuel as the engine instantly encounters a lean condition during normal acceleration.
An accelerator pump also primes the engine before cold starts.
On cold start conditions more fuel in needed to help the engine run properly.
A choke is used to create this additional fuel. The air flow is controlled by choke
at the carburetor�s entrance, before it passes to the venturi. Extra vacuum develops
in the barrel of the carburetor, pulling additional gasoline via the main jet system.
The choke also will hold the throttle bore open slightly to increase the idle speed
to prevent stalling.
Common Problems
The main problem with a carburetor is dirty fuel. This can cause a too rich or
lean condition, meaning there is too much fuel or air to the mixture. The mixture
is normally adjusted by one or more needle valves on the carburetor but dirt can
render these adjustments useless. To check your car's mixture you will need to use
a gas analyzer to test your exhaust gases. This will measure the carbon monoxide,
hydrocarbon and oxygen content of your exhaust. During a normal
smog inspection
the fuel/air mixture is tested and a report generated. When a
tune
up is performed the spark plug end insulator can tell you 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.
Basic maintenance
Changing the
air
filter and
fuel filter will keep dirt/debris from entering the internal workings of the
carburetor. This should be performed each time you change your spark plugs. Spraying
a carburetor cleaner into your barrels and adding cleaning additive to your gasoline
will remove deposits in your jets and in the carburetor itself.
How Does it Work
/ Carburetor
Check Manufacturer Specific Carburetor
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