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How Does it Work /
Choke
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Choke
Questions and Answers
Carburetor Choke Operation
A choke is used in conjunction with a carburetor. It is a valve that opens and
closes and used to restrict air flow. The restriction enriches the fuel/air mixture
to aid in the initial startup of the vehicle. The choke creates a stronger vacuum
to pull more fuel from the jets and into the air/fuel mixture. When the engine warms
up the choke slowly releases and stays in the wide open position.
Carburetor Choke
On older carburetors the choke pulloff was a piston operated by a vacuum in the
choke's housing that held the choke open. The draw back to the piston was that it
had a tendency to stick due to buildup causing a malfunction. Later a vacuum diaphragm
device called a vacuum operated choke pulloff was developed. The choke linkage is
attached to the pulloff to pull open the choke plate when the engine is started.
The fuel mixture will gradually lean out as the choke opens completely.
There are several ways a choke is controlled. One style of choke is controlled
by a temperature sensitive bi-metal spring attached to the choke plate. To heat
this bi-metal spring the choke housing receives heat from a tube near the exhaust
manifold. As the spring is heated it expands and unwinds to moves the choke to the
open position. Others are electrically controlled and heated through an electrical
circuit. Still another style is controlled by heated coolant from the engine. When
the engine has cooled the bi-metal spring contracts and closes the choke.
Adjustments
Depending on the outside temperature the choke may need adjusting. This will
control on how the choke will open and close. Some models utilize screws that you
can loosen and rotate the choke bi-metal spring. This will change the spring's position
and vary the tension increasing and decreasing the operation as needed. Tighten
the spring for more choke in cold weather and lessen the tension in warm. Choke
adjustment can vary, if it is unclear how to adjust your particular choke arrangement
consult a online repair manual.
Basic Checks
If the engine is difficult to start when cold remove the air cleaner and watch
your choke in action (assistance required). Tap the gas pedal once before the engine
running when cold and see if the choke plate closes. If there are carbon deposits
clean as needed and recheck operation. When a choke is operating during warm-up
the engine idle is increased, this keeps the engine from stalling at idle.
How Does it Work
/ Choke
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