Why Your Lawn Mower Won't Start—and How to Fix It

Few things are more frustrating than gearing up to mow the lawn only to find that your mower won't start. With so many potential causes—from stale fuel to a clogged carburetor—it can be hard to know where to begin troubleshooting.

Fortunately, lawn care pros have a systematic approach. Brian Shaunfield, store manager at Lowe's, recommends starting with the basics: fuel, spark, and airflow. From there, check components such as the fuel filter, fuel line, fuel cap vent, carburetor, choke, and safety interlocks to pinpoint the issue.

But which mower components are most likely to cause trouble, and how can you fix them? Here's what to check first.

No Fuel

One of the most common lawn mower dilemmas is a lack of fuel—or other issues related to fuel distribution. "Make sure there's fuel in the tank and that it's fresh," says Shaunfield. "If the mower has been sitting for a month or more, especially over the winter, stale gas is a common cause of start-up problems."

This is because, as fuel ages, it can leave behind sticky deposits that clog the carburetor and other passages in the lawn mower, he says. So if you've left your lawnmower untouched for 30 days or more, then this could be the issue.

Fortunately, if that's the case, it's a pretty straightforward fix. Shaunfield recommends following these steps:

1. Turn the mower off and let it cool completely. 
2. Drain the old gas from the tank. 
3. Inspect the fuel filter and fuel line, and replace if it appears dirty or clogged—or if cracks, clogs, or weak flow are evident. 
4. Refill the tank with fresh fuel that matches your mower's fuel requirements. 

Once this is done, simply reconnect everything and try starting the mower again.

Bad Spark Plug

Spark plugs can also cause start-up issues. "Be sure to inspect the spark plug for any buildup, oil residue, cracks, or other signs of wear," says Shaunfield.

The solution is to either clean your spark plug or completely replace it. He recommends the following steps:

1. Disconnect the spark plug wire. 
2. Using a socket wrench, remove the spark plug. 
3. Inspect the spark plug for buildup, oil residue, cracks, corrosion, or excessive wear. 
4. If the spark plug is only dirty, buy a spark plug cleaner kit to properly clean it. 
5. If the spark plug is damaged or badly worn, replace it with the correct plug for your mower model.  
6. Reinstall the spark plug securely and reconnect the wire. 
7. Start your mower. 

Dead Battery

If your electric lawn mower isn't starting, then one of the first things you should check is if you have a dead battery, says Eric Halfman, go-to-market manager at John Deere. If the mower doesn't crank at all, then you may have a dead battery.

Fortunately, this is an easy fix—make sure your lawn mower is turned off, and remove the battery. You can recharge most batteries with the correct charging device. Make sure you're using the right one for your battery type.

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Other Issues

There are a few other mechanical issues that can cause your lawn mower not to start. Check your air filter for dirt, grass, or oil buildup, says Shaunfield. This can restrict airflow and throw off the fuel-air mixture.

Make sure to check the fuel filter, fuel line, and fuel-cap vent for any clogs or cracks as well. This will stop fuel from reaching the engine. Your carburetor may be stuck or incorrectly set, too—it's always worth checking just to make sure.

Proper Maintenance

Properly maintaining your lawn mower will help mitigate these issues, so they'll likely never even arise in the first place. For example, make sure you're storing your lawn mower in the right place. "Keep the mower in a clean environment away from rodents," says Halfman. "You'll want to charge the battery during the off-season and treat your fuel."

A good care routine will keep the fuel fresh and flowing, and ensure that your spark plug is working properly. Here are a few tips and tricks that Shaunfield recommends:

1. Use fresh gasoline and avoid leaving fuel in the tank for too long. 
2. Add fuel stabilizer before long storage, especially at the end of mowing season. After adding stabilizer, run the mower for a few minutes so treated fuel circulates through the carburetor and fuel lines. 
3. Inspect and clean or replace the air filter regularly to keep airflow unrestricted.  
4. Check the spark plug regularly and clean or replace it if it is dirty or worn. 
5. Inspect the fuel filter and fuel line for clogs, cracks, or weak fuel flow. 
6. Keep the mower deck and engine area clean by removing built-up grass and debris.