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First Thing to Check When Your Lawn Mower Won’t Start

You go outdoors to mow your lawn, but this time your mower won’t start. No matter what type of gas-powered lawn mower you own, it’s easy to get overwhelmed and not know exactly where to start looking for the problem. Because there are so many items that can affect the reason your lawn mower isn’t starting, it’s hard to know just where to begin.

The first thing to check when a lawn mower won’t start is the condition of your spark plug and air filter. Confirm the lawn mower is getting fuel to the engine by checking the fuel supply. A lawn mower won’t start when the engine does not receive the air, fuel and spark it requires to form a combustion.

I have listed the items below along with links to more information on finding and fixing your starting problem. Note: If your mower is new or is being used for the first time since storage, check to confirm the fuel shut-off valve is open allowing fuel to flow out of the fuel tank. The fuel supply may have been shut off using this valve when transporting or storing a lawn mower.

Lawn mower won't start

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing or operating. Consult a professional if you don’t have the skills, knowledge or are not in the condition to perform the repair safely.

The First Things to Check on Your Lawn Mower When It Won’t Start

No Fuel in the Lawn Mower’s Fuel Tank

This is the most simple thing to check on the mower. A lack of fuel is an obvious reason why your lawn mower won’t start. Everyone knows a gas-powered lawn mower requires gas to run. The fuel tank can be low on fuel because you forgot the last time you filled up your mower or you developed a fuel leak depleting the amount of fuel in the tank.

When you find your fuel tank is empty or low on fuel, fill it with fresh fuel. Look over your fuel system for leaks coming from the fuel filter, fuel lines, fuel pump or carburetor. For help finding a gas leak on your lawn mower, read “10 Reasons Your Lawn Mower Could Be Leaking Gasoline“.

Dead Battery on a Lawn Mower

A dead battery will keep your lawn mower from starting. Check your battery using a volt meter. A fully charged 12-volt battery will read 12.7 volts. Charge a battery that isn’t fully charged. If you find your battery won’t hold a charge, it’s time to replace it with a new battery.

Bad Spark Plug in a Lawn Mower

The spark plug is a component that can become dirty and covered in dirt, carbon and oil. A dirty spark plug can cause intermittent spark issues where the mower may not start or run. In addition to a dirty spark plug, a plug that is damaged and has a broke porcelain or burnt electrode can cause a lawn mower not to start.

Remove the spark plug from the mower using a 3/4″ or 5/8″ socket wrench. The size required depends on the model engine used in your lawn mower. Inspect the spark plug’s condition.

If the spark plug is lightly dirty, you can clean it using a wire brush and reuse it. However, if the spark plug is dark in color or you find a burnt electrode or broken porcelain, you must replace it with a new plug. I choose to replace my spark plug annually to keep it in good condition.

If I suspect I have a spark plug problem, I always just replace it since it’s an inexpensive part directly responsible for keeping the engine running at it’s best.

Before installing a cleaned or new spark plug, confirm the plug is gapped according to the engine manufacturer’s specification. Install the spark plug and securely attach the spark plug wire to ensure it is making good contact. A loose spark plug wire or an incorrectly gapped spark plug can also cause your starting problem.

Plugged Air Filter in a Lawn Mower

The air filter can restrict access to clean air when it becomes plugged with dirt and debris. Because your mower kicks up a lot of dust and debris when mowing, the filter can become clogged when it isn’t cleaned or replaced regularly. A plugged air filter not only can prevent your lawn mower from starting, but it can also cause your mower to overheat, smoke and damage the engine.

Start each mowing season with a new air filter. Your air filter maintenance doesn’t stop here. You must check and clean it a few times throughout the season. Follow the instructions in this guide for instructions on cleaning the type of air filter in your lawn mower.

Test for Lack of Fuel to the Engine

If your mower still doesn’t start after confirming you are running a good clean spark plug and air filter, it’s time to make sure you’re getting fuel to the engine. Old fuel running through your lawn mower can leave behind sticky deposits and a varnish that will cause fuel restrictions in the fuel system. When there isn’t a sufficient supply of fuel, your mower will not start.

To identify whether or not you have a fuel supply problem, spray carburetor cleaner into the air intake to see if your mower will start and run temporarily on the carburetor cleaner. Never use starter fluid. Find out why in “Don’t Use Starter Fluid on a Lawn Mower (Use This Instead!)“.

Steps to Confirm a Fuel Issue in Your Lawn Mower Using Carburetor Cleaner:

  • Remove the air filter housing cover.
  • Remove the air filter being careful not to knock any dirt into the air intake.
  • Wipe out any dirt remaining in the air filter housing.
  • Spray carburetor cleaner into the air intake.
  • Start your lawn mower.

If your lawn mower starts and runs temporarily, you have confirmed you have a problem preventing your engine from getting fuel. Check the fuel line, fuel filter, fuel pump and carburetor. Read more about isolating your fuel restriction problem and making the necessary repairs in “Your Lawn Mower Isn’t Getting Fuel: Fix it NOW!“.

Full List of Items That Can Keep a Lawn Mower from Starting

While the above list are some of the most common reasons a lawn mower won’t start, I have compiled a list of more items in “Reasons Your Lawn Mower Won’t Start“. You will find the cause of your starting problem along with solutions for repairing the problem so you can get back to mowing.

Still Having Problems with Your Lawn Mower?

Lawn mower ownership doesn’t not come without its frustrations. Own a lawn mower long enough, you are bound to run into many lawn mower problems including starting, smoking, leaking, cutting and overheating.

For a list of the most common lawn mower problems and items that can cause them, check out my guide “Common Lawn Mower Problems: Solved!