Mercedes Mullins
The choke on a carbureted car restricts airflow, thereby causing extra fuel to be pulled in when it is closed. This enriches the mixture, making it more combustible and easier to start. Fuel-injected engines do not have a choke, but the computer makes the engine run richer when cold. This is done by firing the injectors for longer at startup.
| Characteristics | Values |
|---|---|
| Purpose | To start the engine when it is cold |
| Mechanism | Restricts airflow, creating a higher vacuum, which results in more fuel being drawn in |
| Fuel | The choke adds fuel directly from the float bowl through a small metering orifice to the inlet air stream on the engine side of the carburetor slide valve |
| Fuel Injection | The injectors are fired for longer at start-up |
| Carburetor | The choke is a valve on the carburetor that regulates how much air gets injected into the combustion chamber along with the fuel |
| Throttle | The throttle controls air intake, which in turn varies fuel intake |
| Fuel Enrichment | The choke enriches the fuel-air mixture, making it more combustible and easier to start |
| Lean Mixture | More air and less fuel |
| Rich Mixture | More fuel and less air |
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What You'll Learn
Choke levers are used for a cold start
A choke lever restricts airflow, thereby enriching the fuel-air mixture. This is done by limiting the amount of air that mixes with the fuel, creating a 'rich' mixture. This is a mixture with a higher proportion of fuel to air, which is more combustible and easier to ignite. Therefore, the choke lever is used to make the engine more combustible when it is cold, helping to start the engine.
Choke levers are particularly useful for motorcycles. For example, a BMW motorcycle has a choke lever on the left-hand side of the handlebar, which is used for a cold start. The choke lever is not used when actually riding the motorcycle, only when starting the engine from cold.
In fuel-injected engines, the choke is sometimes replaced by a fast idle lever, which is used to start the engine from cold. However, this is not a true choke, as it does not restrict airflow. Instead, the computer makes the engine run richer when cold.
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Choke works by limiting the amount of air that mixes with the fuel
Choke valves, also known as "chokes", are devices that restrict airflow into the carburetor of an engine. This causes the fuel-air mixture to be "richer", meaning there is a higher ratio of fuel to air. This is because, with less air in the mixture, more fuel is drawn into the engine. This is due to the higher vacuum created by the choke valve, which causes a greater amount of fuel to be drawn in through the inlet tube.
Choke valves are particularly useful for starting cold engines as the richer mixture is more combustible and easier to ignite. This is because gasoline does not evaporate well within a cold engine, so by limiting the amount of air, the choke valve allows the engine to warm up. Once the engine is warm, the choke valve can be opened again to allow for normal operation.
Choke valves are found in naturally aspirated engines, including small portable engines, motorcycles, small propeller-driven airplanes, riding lawn mowers, and normally-aspirated marine engines. They are also used in the extraction of petroleum and other heavy-duty fluid handling contexts.
In fuel-injected engines, there is no carburetor, so a choke in the traditional sense does not exist. However, some fuel-injected engines have a "fast idle lever" or "cold start valve" which serves a similar purpose to a choke valve by making it easier to start the engine when it is cold.
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Choke enriches the mixture by restricting airflow
The choke works by limiting the amount of air that mixes with the fuel. More fuel and less air makes for a rich mixture. As you cannot have combustion without oxygen, by making the mixture richer, it makes for a more combustible fuel, and easier to start. Hence the purpose of choking your engine when it is cold. The cold start valve for fuel injection simply sprays gas to aid starting.
The choke on a carbureted car causes extra fuel to be pulled in when it is closed. Closing the choke valve lets in less air, and once the engine is warm, you open the choke valve again. This is achieved by increasing the vacuum on the fuel inlet tube, which results in more fuel being drawn in. This is why some setups are known as "enrichers" instead of "chokes".
In the case of fuel-injected engines, the computer makes the engine run richer when cold. This is done by firing the injectors for longer at start-up.
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Choke valves are used to control airflow
In a car engine, air and fuel are combined in the fuel injection system. When the engine is cold, the fuel tends to condense and stay as a liquid on the walls of the carburetor. The choke valve is used to limit the amount of air being let into the carburetor, creating a richer mixture of fuel and air. This richer mixture is more combustible and so helps with cold starts.
The choke is essentially a valve on the air intake that regulates how much air gets injected into the combustion chamber along with the fuel. By closing the choke, the airflow is restricted, and this generates a greater vacuum on the fuel inlet, drawing in more fuel. This is why choking an engine by restricting the airflow results in a richer mixture.
On a motorcycle, the choke lever is usually found on the left-hand side of the handlebar. This is used to control the air-fuel mixture and is particularly useful for cold starts. It is important not to leave the choke lever in an advanced position when riding, as this can cause the engine to stall or run poorly.
Some modern fuel-injected vehicles use an automatic choke or a fast idle lever, which is controlled by the ECU. This makes adjustments to the fueling and air mixture, depending on the temperature of the engine.
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Choke is not required for fuel-injected engines
The choke on a carbureted engine works by limiting the amount of air that mixes with the fuel, creating a richer mixture that is more combustible and easier to ignite. This is particularly important when starting a carbureted engine in cold conditions.
However, fuel-injected engines use fuel injectors that are fired longer at startup, ensuring that enough fuel is pulled in without the need for a choke. Additionally, fuel-injected engines may have a throttle body injection (TBI) system, which looks like a carburetor but is controlled by an exhaust sensor and an airflow sensor to manage the airflow and fuel intake.
It is worth noting that some fuel-injected vehicles, such as certain motorcycles, may still have a choke lever or a similar mechanism. However, these are typically not true chokes but rather fast idle levers or enrichment circuits that assist with cold starts by increasing the idle speed.
In summary, while a choke is essential for carbureted engines to enhance fuel-air mixture during cold starts, fuel-injected engines have alternative systems in place, such as cold start valves, extended fuel injector operation, and TBI, that eliminate the need for a choke.
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Frequently asked questions
The choke on a fuel-injected car is a fast idle lever. It is used when starting from cold, and only if the car is having trouble idling.
A choke restricts airflow, which increases the amount of fuel in the mixture. This makes the mixture richer and more combustible, making the engine easier to start.
A choke restricts airflow, while a throttle increases it. The throttle also adjusts the amount of fuel to compensate for the change in airflow.
When an engine is cold, the fuel does not evaporate as well and tends to condense on the walls of the carburetor. By choking the engine, you bring in less air, ensuring there is enough fuel in the cylinder to start the engine.
On a fuel-injected engine, the computer makes the engine run richer when cold. This is the equivalent of choking a carbureted engine.
