How Does it Work / Choke

• Choke Questions and Answers

Carburetor Choke Operation

Introduction

A choke is used in conjunction with a carburetor. It is a valve that opens and closes 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, moving 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, which works on the same principle but uses coolant instead of hot air to engage/disengage the choke. Manual chokes are controlled by a cable in the passenger compartment that allows the operator to adjust how much choke the engine is getting. When the engine has cooled the bi-metal spring contracts and closes the choke

Adjustments

Depending on the outside temperature where you live the choke may need adjusting. This will control 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 an 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 to the floor before the engine is running (Key on) 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, but should decrease as the engine warms up and the choke releases.

How Does it Work / Choke

Check Manufacturer Specific Choke Questions and Answers

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