Automatic Choke: What It Is And How It Works (Automatic Choke)

Hello, and welcome to this article about automatic chokes. I will talk about everything, from how they work to how to adjust them on different kinds of equipment.

And if you want to know what heats it up, I can tell you. Stay tuned to learn more about automatic chokes.

What is an automatic choke

First the formal definition:

A system for enriching the air-fuel mixture in a cold automotive engine when the accelerator is first depressed. The choke plate opens automatically when the engine achieves normal operating temperature.

An automatic choke is a component found in the carburetor of some gasoline engines.

Its purpose is to regulate the fuel-air mixture in the engine by controlling the flow of air into the carburetor.

Modern vehicles have advanced to using electronic fuel injection systems that do not require an automatic choke.

Note: Some "choke valves" are not automatic. Read more on the Wikipedia:

Working Mechanism

The automatic choke operates by using a metal spring that opens and closes the choke plate.

As the engine warms up, the spring unwinds, opening the choke plate and allowing more air into the carburetor.

This helps to maintain a smooth and efficient operation of the engine.

I also included the below information to complement the definition:

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Automatic Choke: Regulating the Air-Fuel Mixture

The specific mechanism used depends on the carburetor design.

Working Mechanism with a Metal Spring

A metal spring is wound in a housing and attached to the choke linkage on one end.

As the engine warms up, it heats the metal spring, causing it to expand and rotate, which opens the choke plate.

This allows more air into the carburetor, resulting in a leaner fuel mixture for cold starts.

The metal spring does not directly open the choke plate, but rather moves a linkage that opens it.

Working Mechanism with a Vacuum Source

In some carburetor designs, an internal vacuum source enters the choke housing and creates a negative pressure (vacuum) on the system.

This causes a bimetal spring to relax and open the choke plate.

The opening of the choke plate results in a richer fuel mixture for cold starts.

Availability of Vacuum-Regulated Chokes

The use of a vacuum source to regulate the choke is not universal and depends on the specific carburetor design.

Adjusting the Automatic Choke on Lawn Mowers and Generators

Honda Lawn Mower

  • Remove the cover on the fuel cap.
  • Slide the automatic choke lever towards the back of the mower.
  • Turn the choke knob until the blade starts to pull away from the ground.
  • Reattach the cover and start the engine.

Onan Generator

  • Tighten the clamp screw behind the choke.
  • Use two screws on the front to loosen the heating plate.
  • Set the choke rod linkage connection at 70 degrees Fahrenheit.
  • Tighten the screws and check the choke operation.

Kohler XT6 Engine

  • Identify the design of the engine.
  • Ensure the choke plate is closed when the engine is cold.
  • Refer to Kohler M18 Service Manual for instructions.
  • Refer to a guide on adjusting Kohler engines with Auto Choke.

Rochester 2 Barrel Carburetor

  • Loosen screws on choke thermostat cover.
  • Turn cover until choke closes against carb throat.
  • Adjust spring tension inside choke housing as necessary.
  • Clean integral choke piston before reassembling.

5.7 Mercruiser

  • Ensure the engine is cold.
  • Loosen the three screws on the choke coil.
  • Rotate the choke coil until it is barely starting to open.
  • Add an electric choke thermostat and wire it to key on.
  • Use a divorced choke cover and hold-down screw.

Note: It is important to follow the specific instructions for each model and to have adjustments made by a qualified mechanic.

Improper adjustments can result in engine damage and reduced performance.

Automatic choke operation

This article provides information on how to use an automatic choke in different types of vehicles.

It can help you activate and use the automatic choke in different types of vehicles.

Activating the Automatic Choke

  • Make sure the vehicle has not been running for at least 4-5 hours.
  • Remove the air cleaner assembly.
  • Depress the accelerator pedal to the floor.
  • Turn the automatic choke element clockwise until the butterfly valves inside the carburetor are standing straight up.
  • Adjust the opening of the choke.

Edelbrock Carburetor

  • The electric choke is powered by the ignition switch or a 12V power source, not the alternator.
  • The automatic choke on an Edelbrock carb is heated by an electrically heated coil, which is powered by wiring it to the S terminal of the alternator.
  • The heat tube for the automatic choke should be connected to the exhaust manifold.

Performance Carburetor

  • Attach the bayonet end of the long electrical lead to the positive terminal on the choke cap.
  • Install the electric choke cap and make sure the metal tab fits into the slot in the carburetor body.
  • The electric choke can be wired to an IGN tab on a fuse block or to the alternator.

302 Ford E150

  • Find a circuit that is hot in the run position and tap into it.
  • Attach the electric choke conversion kit to the carburetor.
  • Set the hook at the end of the coil on either side of the piston stem.

Ford F100

  • Connect the electric choke to the alternator's stator terminal.
  • Ground the connection to the intake manifold.
  • Check the carburetor for compatibility with the F100.

Electric Choke Power Source

  • The most common source of power for an electric choke is a 12-volt ignition source, such as the alternator.
  • Some aftermarket chokes require a full 12 volts to operate, while others may work with 7 volts from a stator wire.

Motorcraft 2150 Carburetor

  • Equipped with an electric choke system that operates using a thermostat.
  • To adjust the choke, loosen and rotate the black plastic housing until the choke plate is nearly closed.-.
  • When the engine is cold, the thermostat closes the choke valve to reduce air flow into the engine, causing an increase in fuel flow.
  • As the engine warms up, the thermostat opens up to allow more air into the engine and reduce fuel flow.

Setting the Automatic Choke in Cold Weather

  • Make sure the vehicle is cold (hasn't run for 4-5 hours).
  • The butterfly should close freely when the engine is cold and the throttle is opened enough.
  • Remove the air cleaner and check the choke plate, it should be open.
  • Depress the throttle once to set the choke plate and give the motor a shot of fuel.

Understanding Their Function and Limitations

An automatic choke is a device found on the carburetor of gasoline engines, designed to facilitate the starting process in cold weather conditions.

Understanding the function and limitations of automatic chokes is important for those who own gasoline engines.

It is also important to consider whether manual or automatic choke is preferred, and to understand the available options for conversion.

FunctionalityWhen the ignition key is turned to the start position, the automatic choke is activated, and the engine receives a richer fuel mixture. This richer mixture helps the engine to start easily in cold weather.
DisadvantagesHowever, automatic chokes also have some drawbacks compared to manual chokes, including a lack of control and potential for malfunctioning.
Manual Choke ConversionFor those who prefer more control, it is possible to convert an automatic choke to manual using a conversion kit. These kits can be purchased online from retailers such as Amazon, Walmart, or from automotive stores. In manual chokes, the choke must be slowly opened by hand by someone inside the car.
Types of "Automatic Chokes""Automatic chokes" can be of three types: thermal, vacuum-operated, or electric.

Maintaining and cleaning the automatic choke

Cleaning the Automatic Choke on a 2006 Arctic Cat 400 4x4

  • Remove the choke.
  • Clean the choke.
  • Check continuity of coil with an ohmmeter.
  • Clean carburetor if necessary.

Starting a TaoTao 150 ATV with an Automatic Choke

  • Release parking brake.
  • Turn on key and run switch.
  • No choke lever needed.

Replacing an Automatic Choke

  • Remove choke assembly and linkage from carburetor.
  • Purchase manual choke conversion kit (if desired).
  • Adjust kit for proper operation.
  • Mount warning light and choke control knob on dash.
  • Remove electric choke components from carburetor.

Note: Replacement parts can be purchased from retailers such as Amazon.

The process of removing the automatic choke takes approximately 5 minutes.


Automatic Choke Adjustment for Rochester 2 Barrel Carburetor

To ensure proper operation of your carburetor's automatic choke, follow these steps:

  1. Loosen the screws on the choke housing.
  2. Adjust the choke plate until it closes all the way when the engine is cold and the throttle is moved.
  3. Tighten the screws on the choke housing to secure the choke plate in place.
  4. Check that the choke plate opens fully when the engine warms up.
  5. Make further adjustments as needed.

Automatic Choke on a Lawnmower

The automatic choke on a lawnmower is an important component that helps the engine start more easily in cold weather.

Here's how it works:

  1. The choke opens when the engine is cold, allowing more fuel to be drawn into the engine.
  2. The choke is usually opened by a spring-loaded mechanism and closed by either the airflow from the flywheel or a thermostatically controlled valve.
  3. It is important to ensure that the choke is in the open position when starting a cold lawnmower.
  4. Allow the engine to warm up before engaging in any mowing activities.

Note: Running with the choke on can cause damage to the engine, so make sure to follow these steps carefully.

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