How does an electric choke work? Let us explain.
Engines generally don’t run smoothly when cold; you might notice a rough idle in modern engines.
But these modern motors have computers to adjust the fuel-air ratio for quick warming.
Old engines use carburetors to mix air and fuel before injecting the flammable mix into the combustion chambers.
And these carburetors relied on manual or electric chokes to reduce air in the fuel mix to warm the engine faster to optimal operating temperature.
Let’s look at how these electric chokes work.
What Is a Choke?
A choke plate or blade is a device that restricts airflow into the engine by covering the primary barrels.
So it does not control the fuel flow. Instead, it regulates the flow of air. And it ensures the engine gets a rich fuel mix during a cold start.
As the engine heats up, the choke gradually opens, allowing more air supply.
This leaner fuel-to-air ratio makes the engine run more efficiently and at lower temperatures.
A dual-chamber car carburetor with a choke (the open flap)
If you live in warm climates, such as around the tropics, your carbureted engine might not need a choke.
But if you live in cold areas, get the most suitable choke for your vehicle. Let’s look at the choke types.
Types of Choke Systems
Carburetor engine chokes come in two types.
Manual
As the name suggests, a manual choke requires human input to adjust the air-fuel ratio.
So vehicles with this choke have a knob or lever inside the cabin that connects to the choke lever.
This choke lever is usually on the side of the carburetor.
A manual choke opening switch in a carburetor for cold starting
When starting the vehicle, you have to pull the lever or turn the knob to restrict the flow of air.
And as the engine warms up, let go of the lever or knob gradually.
As you can imagine, this system is inconvenient but gives more control.
Automatic
Automatic chokes use metal springs to open and close the choke plate.
Wound inside the housing, this metal spring attaches to the choke plate linkage on one end.
When starting, this spring is cold and closes the choke, meaning the engine runs rich (more fuel, less air).
As the engine warms up, the springs warm, gradually expanding, rotating, and opening the choke.
A carburetor’s choke valve
These automatic chokes come in three types.
- Hot air/integrated heat choke: This device features a metal spring in its housing, with a tube connecting to it. The pipe directs hot air from the exhaust to warm the spring or thermostat, which opens the choke. Some can have hot water jackets running on or through the thermostat to heat and open the choke.
- Divorced choke: These choke units feature thermostats mounted in the intake manifold, with a tiny rod connecting this thermostat to the choke lever in the carburetor. When the engine runs, the intake manifold becomes hot. These high temperatures heat the spring/thermostat, which opens the valve to allow more air into the carburetor.
- Electric/power choke: As the name suggests, this choke unit uses electrical power to open or close the valve.
How Does an Electric Choke Work?
Electric chokes are solenoid valves that block the flow of air when energized.
This solenoid operates based on the voltage fed to it by the vehicle’s battery. It consists of four parts.
A motorcycle engine carburetor
- Plunger: Features two ends with one protruding outside the housing
- Sleeve: Positioned centrally in the housing with the inner side of the plunger fitting inside the sleeve in the housing
- Solenoid/choke coil: An electromagnet/coil of wire. This coil wraps around the sleeve and has positive and negative terminals that connect to the battery (voltage source).
- Choke housing: A metal or plastic casing with epoxy stuffed between it and the solenoid to insulate the current in the copper coil from getting outside
Both the sleeve and plunger have a conductive metal construction.
The solenoid wrapped around the sleeve makes it an electromagnet when a voltage gets applied.
This electromagnet pulls the plunger to block the flow of air when energized.
As the engine warms up, the power going to the solenoid eases, which releases the plunger.
This action opens the choke valve, allowing more air into the carburetor, resulting in a leaner fuel-air ratio.
Electric Choke Wiring
The voltage intensity applied to the solenoid determines how far the plunger will move, which regulates the airflow.
So instead of having an on/off mechanism, the timing system adjusts the voltage going to the solenoid to have a gradual choke valve opening.
Carburetor cleaning and repair
Since old vehicle engines with carburetors didn’t have computers, manually adjust the choke’s timing to get it in sync.
So when installing this device, first mount it to the carburetor’s air intake. Use a choke rod or tube to link the device to the carburetor.
Once installed, connect the choke’s positive and negative terminals to a 12-volt power source (vehicle’s battery) via the ignition system.
Link the positive blade terminal to the positive terminal in the battery and the negative terminal to the ground source.
The electric choke might need adjustment to ensure it opens the valve at the right time.
If it opens too soon, your car will experience stumbling, difficulty starting, stalling, and backfiring.
And if it opens late, your vehicle will have poor fuel economy, emit black smoke (too much fuel), and have engine misses.
Adjusting the device involves moving the timing. Open the three locking screws on the choke cap, then rotate this cap clockwise if the valve opens late.
If it opens too early, turn the cap counterclockwise. Rotate this cap one notch at a time until you get the timing right.
The adjusting screw on a carburetor in a gas generator
Electric Choke Timing Adjustment Mechanisms
The electric choke timing mechanism can be a center pointer or a bimetallic heating element.
Center pointers usually have index marks on the thermostatic caps and mountings.
What if the Electric Choke Fails To Open?
Electric chokes rarely fail. But worn-out air filters around the plunger can cause dust accumulation, resulting in a sticky plunger.
Internal shorting in the solenoid can also make the plunger fail to work.
If the plunger fails in the closed position, it will restrict airflow to the carburetor, causing the engine to run rich after warming up.
This rich air-fuel ratio can clog the spark plugs and cylinders, increasing the risk of engine failure.
Also, it will give your vehicle poor fuel economy and reduced power output.
Wrap Up
Some vehicles still have old carburetor engines, so you might encounter one, especially if you enjoy working on vintage models.
If the car exhibits any of the signs explained earlier, you can check the choke.
And if it doesn’t have an electric one, try replacing it to get the best-automated air-fuel mixing in the engine.
