Is My Engine Choke Symbol On or Off on My Lawn Mower? Everything you need to know

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If you are finding it difficult to determine if your lawn mower’s engine choke symbol is “On” or “Off”, you aren’t alone.

The engine choke symbol is often difficult to find and/or read as it can fade or get covered in dirt and debris over time. Likewise, if your lawn mower choke is without a bulb, or the bulb is not working, it can also be difficult to know if the whether you’ve switched the choke symbol On Off.  

I’m here to teach you a little about the basic function of a choke, help you determine which symbol is Off, which is On, and what to do if you can see your visual signals.  

Where Is the Choke Located On a Lawn Mower?

The choke valve is typically found on the engine body or as a lever on the handle.  There are a variety of gas lawn mowers on the market and the location of the choke valve will vary from machine to machine. 

For example, if your lawn mower has a butterfly valve the choke valve will likely be positioned directly in the manifold. The same is true for other gas machines like snowblowers, generators, and stick edgers.  

man working on lawn mower

What Does Choke Control Do On a Lawn Mower Engine?

The choke in any electrical power equipment controls the air flow that enters the engine’s cylinders and mixes with the liquid fuel mixture.

This is true for both 2-cylinder and 4-cylinder machines. 

When the choke is turned On, your carburetor is blocked by a small piece of metal or plastic. It completely restricts or “chokes” any air flow from moving into the engine, and it controls the air-fuel ratio as a result.

What Happens When You Close the Choke Valve?

When you close the choke valve on your machine, you send more fuel to the engine cylinder and restrict or “choke”  the flow of air.  The extra fuel helps heat the engine to the temperature needed to start an engine. 

How Do You Tell if The Engine Choke Is On or Off?

Finding your engine choke’s On symbol and Off symbol can look a little different from machine to machine.

Your gas-powered machine may also include an auto choke. Some machines have a choke light, while others have hard-to-read symbols or markings.

You are out of luck if you are looking for consistency! 

choke symbol

What’s The Symbol For Full Choke?

If you’re lucky, your machine has a choke trigger or lever near the engine labeled:

  • Full choke
  • Half choke
  • Run

If, however, you are not so lucky, and your machine doesn’t clearly state this then the choke is likely labeled in one of the following ways:

  • Start” –  this is commonly used to indicate that a choke is engaged and ready to start a cold engine.
  • Closed” – if you see this word near the engine control module, then you have a closed and engaged choke.

If all you see is a switch – usually red, but occasionally blue – then this relates to the choke valve.  On either side will be an “I” and an “O”:  

  • I” – the choke is engaged and the air supply will be restricted to the carburetor. Switch to the “I” position to start. 
  • O” –  the choke is not engaged.  Switch to the “O” position after your machine is warmed up. 

Still can’t figure it out? When all else fails, check your lawn mower manual. This should include information about the location of your choke, what position it should be in to start, and may have some recommendations for how long you should run your machine with the choke open before turning it Off. 

What’s The Symbol For Half Choke?

Two-cycle engines commonly feature a half choke option. As you have probably guessed, this allows you to open your choke halfway or have it closed halfway. 

The reason for this is many lawn mower’s (with or without this feature) will sometimes die out if you quickly move from full choke to no choke. 

Using the halfway feature allows you to start your machine and then allows your machine to adjust to a reduced air flow. I have an old snowblower that if you start up and then kill the choke, immediately sputters out. If, however, I start in the full choke, then move to the half choke position and let it run for a minute or two before turning it Off, runs like the day I brought her home.

So how do you know if your lawn mower has a half choke?

  • If your machine has a half choke symbol, it will be in a third color on your choke dial – right in the middle.  This spot indicates when your choke lever is halfway open. 
  • If your machine doesn’t have a half choke symbol, don’t worry. Just slide the choke lever halfway between the open and closed position. 

During Operation

Leaving the Choke On During Operation

Many machines will see a breakdown in power and performance if the choke lever is left in the On position. I do not even recommend leaving your choke in the half-choke position. 

Check the choke if you are operating your machine, and it doesn’t seem to have the same giddy-up as it was the last time you used it.

lawn mower

When To Turn The Choke Off During Operation?

In general, you will want to turn the choke Off when the machine is warmed. When will vary from lawn mower to lawn mower. 

Some machines will give you visual or auditory clues that it is warmed up such as sputtering or black smoke coming from the engine compartment. This is usually a good sign your machine is warmed up, ready to have the choke turned Off and used.

For example, I have a lawn trimmer that will tell me when she is ready. Because I have used this machine for so many years, I can hear the cold engine slowly warm up, and I know exactly what it sounds like when it’s time to change the choke position.

Keep in mind that turning your choke Off too soon will also stop the engine from running.

engine choke symbol

Is It Bad To Leave The Choke On?

Ideally, you will only use your choke when it is absolutely necessary as overusing the choke can permanently damage your engine.

As you become familiar with your equipment, you will get a feel for when your machine is warmed up and ready to go.

Remember, that the longer your lawn mower choke is in the full “On” position, the more fuel your machine will use. This wastes money, isn’t great for the environment, and can eventually create costly problems for your gas powered machine. 

Should I Leave The Choke On or Off for Storage?

You will also want to turn your choke Off when storing your equipment, especially for longer periods of time.

Setting the choke symbol to Off also keeps debris and dust from getting inside parts of your machine- another proactive maintenance idea.

I always turn my choke lever Off, so I know when it’s time to heat up the cold engine again; I don’t have to guess if I turned it On or Off. 

Engine With a Choke Switch – Troubleshooting Tips

Why Will My Machine Only Run With the Choke On?

Back in my twenties, when I wasn’t really smart, I had a trimmer that would only run when the choke was in the “On” position. By the end of the summer, the engine burned up on me, and I cursed the manufacturer and vowed never to buy their product again.

My grandfather asked to take a look at it. Within about 30 seconds, he diagnosed the problem: user error. 

The problem wasn’t the machine; it was that some dummy (me) had used the trimmer to remove heavy grass and a small brush in the spring.  The fuel was nasty looking and the air filter was completely matted with grass. 

The moral of the story?

If your machine only runs with the choke wide open, you have debris somewhere, creating an environmental choke and preventing air flow to the carburetor.

The fuel lines could be blocked, a dirty air filter, or a grimy fuel filter clogging the fuel supply.

You will want to check these out before you end up ruining your equipment. 

man mowing lawn

Why Won’t My Machine Start?

If you have trouble getting your electrical equipment started and have tried opening and closing your choke:

  1. Check the fuel tank: It’s always a good idea to check the fuel tank. Ensure you are using fresh fuel and that your fuel supply lines and filter are clean. Blockage in fuel lines will cause your machine to run poorly or not at all. 
  2. Check your air filter: Your air filter should be free of dust and debris, allowing for clean air intake.
  3. Check if your machine is overprimed: If your machine has a primer bulb, ensure you haven’t overprimed and added excess fuel to your lawnmower, trimmer, gas generator, or snow blower engine. Clear air intake is critical for a properly functioning machine. 
  4. Check your choke lever: From time to time, check quickly to see if your choke lever or dial arrow is functioning properly. 


Q. What Position Should the Choke Button Be In?

A. When starting your machine, the choke would be in the start or On position. 

Q. Can a Warm Engine Start With the Choke Off?

A. If you have been running your machine for a while, you may be able to restart it without using the choke.  You will not harm your machine if you turn the choke back On to start it up. If it’s been running a while, you can probably shut it Off soon after starting.

Here’s an informative video on how to fix your mower just in case it only runs with choke on:

Fix Your Mower - Only Runs With Choke On

Final Thoughts

You now have a better understanding of what a choke is and what it is used for, and hopefully, knowing how to use it can help you spot other problems that your machine may encounter. Using your machine’s choke properly can save you time and fuel and hopefully help you avoid expensive repairs or replacement costs.