What Does a Choke Do On a Lawnmower?

Any homeowner who mows their lawn is familiar with the rev of the engine when you start it up. During the moment between starting the engine and pushing forward to cut the grass, the choke plays an essential role in getting things moving.

Some engines have automatic chokes, and others have manual ones. Your experience with your mower’s choke may vary, but all combustion engines have a mechanism to control the ratio of gasoline to air in the carburetor.

How Does A Choke Work On A Lawn Mower?

Choke levers are common on small engines like the ones in lawn mowers. They allow or restrict airflow into a carburetor for a dense fuel to air ratio, which burns at a high temperature to start the engine. Instead of a choke, some engines have a primer bulb that effectively raises the fuel ratio by injecting extra fuel into the combustion chamber.

The choke valve, or throttle, on a lawnmower, gets its name from its purpose: the valve “chokes off” or “throttles” the flow of air into the combustion chamber of the engine’s carburetor, allowing the fuel to heat up quickly and get the engine started.

When the engine warms up, it will burn gasoline more easily than it does when the metal is cool. Starting an engine when the metal is cool is known as a cold start.

Should The Choke Be Open Or Closed When Starting Lawn Mower?

Should The Choke Be Open Or Closed When Starting Lawn Mower

The choke lever is closed at start-up to restrict the air intake in the combustion chamber. The difficulty of getting fuel and the engine heated up to operating temperatures is solved using the choke and a spark plug. The spark plug ignites the gasoline, which burns at a higher rate from the low amount of air and heats the engine quickly.

When the air to fuel ratio is low, it’s known as running “rich.” A rich fuel mixture burns quickly to keep the combustion going up since it has less air in the chamber to heat up. Warm air in the combustion chamber keeps the temperatures up to deliver a steady stream of power to the mower.

Is It Bad To Run A Lawn Mower With The Choke On?

The choke doesn’t need to be on once the cold engine is warmed up after a few seconds. If it stays on, the fuel will continue to burn rich, use more gasoline over less time, and potentially overheat the engine.

This is why regulating the air intake in combustion engines is important. The right amount of air in the mixture will heat up as the fuel combusts and keep the engine warm as the engine pulls in air consistently.

When there is too much air in the mixture, it can cool down too quickly and cause the engine to sputter, stall, or shut off from a lack of energy. This high air to fuel ratio is known as a “lean” mixture, and in the right balance, will be efficient and keep the engine running smoothly.

Since air intake is important for fuel economy and engine health, the choke will be off or open while running normally.

Is My Choke Manual or Automatic?

Some mower models have a manual choke, where a handle, lever, or button is connected to the spring tension on the valve to open or close it. Other models have an automatic choke that is temperature-sensitive, activates at ignition, and will open and close as necessary on its own.

Is My Choke Manual or Automatic

Engines are increasingly being made with automatic chokes, including common engine manufacturers like Honda, and Briggs and Stratton, which you’ll find in top mowers like Craftsman and Husqvarna.

However, manual chokes on mower engines are still popular among users who like to be able to adjust their machine’s settings closely.

What Control Symbol Indicates The Choke?

The symbol for the choke varies by manufacturer, but there are a few that are widely used:

  • One type looks like a propeller in between two lines, representing what the choke looks like in the carburetor. When it’s tilted, it’s in the closed position, and when vertical, it’s open to allow airflow.
  • Another common symbol is the rabbit and turtle pair, where the rabbit means open or high energy, and the turtle indicates a slow, steady fuel.
  • Some models of mower don’t have a symbol but rather have choke controls that are labeled “open/close,” “on/off,” or” push/pull.” In any case, your mower’s choke symbol is clarified in your model’s manual.

Where Is The Choke On My Mower?

Where Is The Choke On My Mower

When you have a manual choke on your mower, you can locate it by following the cable from the trigger to the engine. If you have an automatic choke, you’ll find it near the air intake and next to the carburetor, the same location as a manual one.


Author: Matt Hagens

Hi, I’m Matt the owner of Obsessed Lawn. I love to be outside working on my lawn, planning my next project. I created this website to help people like you find the best products for yard care and great advice. Learn more about me and find me on Facebook.