Reasons Your Lawn Mower Won't Start and How to Fix Them

Quick and easy ways to diagnose and fix a malfunctioning lawn mower

If your lawn mower isn’t starting, don’t worry—this is one of the most common complications people run into when it comes to lawn care, and the problem is usually very easy to solve. If it won’t start at all, you may be out of gas, have a clogged air filter, or stuffed mower deck. It could also be an issue with your deadman’s switch. If the mower is starting but shuts off soon after, it could be a problem with the spark plug, fuel vent, or gas quality. Whatever the cause, we’ll show you how to identify and fix the issue.

1

Confirm you have gas.

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Start with the obvious and make sure the tank isn’t empty. If you can’t remember the last time you filled the gas tank, just rule this out first before you start tinkering with the mechanical components of your lawn mower. Check the tank’s fuel levels and add gas if it’s empty.
- If you have a corded mower, make sure the outlet you’re using is good by testing it with a phone charger or some other item you know works.
- If you have a riding mower, check the oil tank, too. Riding mower engines often require dedicated oil, and the tank might be empty.

2

Check the air filter.

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Clean or replace the carburetor filter if it’s dirty. A blocked-up filter will block the engine from starting. Refer to your manual to locate the air filter (it’s usually in a container on the side of the engine, near the primer button). Remove the filter to see if it’s dirty. If it’s a paper filter, replace it with a fresh one since these are designed to be discarded periodically. If it’s a plastic, foam, or metal filter, clean it thoroughly with dish soap and water.^{[1]XResearch source}
- If the filter is damaged, replace it.
- Mower filters aren’t universal, but most companies use the same filter for multiple models. So, if you’ve got a Black & Decker mower, a standard Black & Decker filter should fit.

3

Empty the mower deck.

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If the mower deck is full of clippings, the starter rope won’t pull. The mower deck is the disc-shaped area where the blades spin. If that area is clogged, pulling the starter rope will be impossible (or extremely difficult). Flip the mower over and carefully remove any clumps of grass before trying to start the engine again.^{[2]XResearch source}
- Those blades are sharp, so be careful and don’t touch the blades directly as you work.
- If you’ve got a bag attachment and that bag is full, the grass won’t have anywhere to go when you run the mower and it’ll just clog the deck. Empty the bag if it’s full.

4

Inspect the spark plug.

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Clean the spark plug if it’s corroded, or replace it. The spark plug is responsible for providing the spark that ignites the fuel and air in the engine, but without that spark, the mower won’t start. Refer to the manual to determine where your spark plug is located. Use a socket wrench to remove that plug and inspect it. If there’s corrosion, clean the spark plug before reinstalling it. If it still won’t work, purchase a replacement spark plug.^{[3]XResearch source}
- To identify which spark plug you need, search online for one specifically designed for your mower. A replacement plug shouldn’t run more than $4-10.
- To clean a spark plug, spritz the corrosion with brake cleaner and wipe it dry with a clean cloth.

5

Clear the fuel vent.

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If the mower starts, sputters, and quits, it’s likely the fuel cap vent. Most gas lawnmowers use a vented air cap that is designed to let excess pressure out of the fuel tank while providing enough airflow for the fuel to pour smoothly into the engine. If that cap is dirty, the mower will start then shut down. Remove that cap and clean the vent by rinsing it out with water. If you’re struggling to clean the vent, use a clean paintbrush to wipe the opening.^{[4]XResearch source}
- If you replace the cap after cleaning it and the mower continues to turn on and shut down, the cap likely needs to be replaced.

6

Replace the gas.

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If you’re still struggling to start it, consider the age of the fuel. If it has been a long time since you’ve used your lawn mower, the gas may have just gone bad. You can tell the fuel has soured if the mower has trouble starting but the starter rope isn’t hard to pull, the mower won’t stay on, it idles rough, or weird noises are coming from the engine. Simply drain the tank and refill it with fresh fuel to see if that fixes the issues.^{[5]XResearch source}
- You can usually smell bad gas, too. Expired gas won’t have that pungent, strong odor you normally have with fresh fuel.
- If you go 6 to 12 months at a time without needing to refill the mower’s gas tank, add a fuel stabilizer to the tank. The stabilizer will extend the life of the fuel in the tank.

7

Close and reopen the shutoff valve.

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A sticky or stuck shutoff valve will keep fuel from flowing freely. Some lawnmowers have a shutoff valve designed to cut the flow of fuel off if the engine catches fire or the mower starts leaking. If that valve gets stuck or gunk builds up inside of the rim of that valve, it can throttle the flow of fuel and make starting the mower impossible. Try opening and closing that valve repeatedly. This should shake off any debris and improve the flow of fuel.^{[6]XResearch source}
- You can also gently tap each side of the fuel line with a wrench or screwdriver to shake loose dirt trapped inside the fuel line.

8

Inspect the safety release cable.

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The oddly named “deadman’s control” may be the culprit. Every modern mower has a safety feature called the “deadman’s control.” It’s designed to keep the mower from turning on and running when someone isn’t present to monitor the mower. If you don’t engage the deadman’s control while you start the mower, the engine won’t actually crank. Refer to your manual if you can’t figure out how to engage the control while starting the mower.^{[7]XResearch source}
- Typically, you engage the deadman’s control by pulling a handle and holding it down against the hand railing. On some mowers, you push a button down on the hand railing.

9

Solicit some help.

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At this point, it’s best to just contact a lawn mower repair person. If you’ve checked all of the major components already and tried to complete a few repairs but the mower still won’t start, contact a professional. Look online to find a lawn mower repair company near you. It shouldn’t run more than $40-90 to get some help.^{[8]XResearch source}
- In a pinch, you can even reach out to a landscaping firm for help. A lot of mom-and-pop shops have so much experience with mowers that they may be able to help.

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Tips

If you have a riding mower and it won’t respond to anything when you crank the engine, it’s possible that you need to charge the battery. If that doesn’t help, it likely needs to be replaced.^{[9]XResearch source}
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If your mower is nearing the end of its life and you’re suddenly in the market for a new lawn mower, consider going electric! They’re a lot cheaper than gas mowers, and you won’t need to fiddle with pulling any starter ropes or refilling gas.^{[10]XResearch source}
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