As a lawn mower owner, the chances you run into your mower not starting is pretty high. A lawn mower requires air, fuel, and spark to run. There are many different items that can keep your mower from getting one of these requirements.
A lawn mower won’t start when there is insufficient or bad fuel; a dirty spark plug; a plugged air filter; a clogged fuel system; a dirty carburetor; a bad battery; loose or corroded wires and terminals; a bad starter solenoid; or a bad safety switch.
Many of these items can easily be troubleshot and repaired by you. Follow the safety precautions in your operator’s manual to prevent injury while working on your mower.
If you are unsure of your mechanical skills, it’s best to take your lawn mower to a professional repair shop to prevent further damage to the mower or personal injury.
This guide refers to gas-powered lawn mowers. While gas and diesel mowers share many of the same causes for not starting, there are several differences. Have a diesel lawn mower? Read Reasons a Diesel 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, or knowledge or are not in the condition to perform the repair safely.
|Cause||Reason for Problem||Solution|
|No gas in the fuel tank||Fuel tank is empty||Fill with fresh fuel|
|Bad or old fuel||Fuel breaks down overtime making your fuel less efficient and prone to clogging the fuel system||Drain the fuel tank and fill it with fresh fuel. Use a fuel additive like Sea Foam to stabilize the fuel and assist with cleaning the fuel system. Use the right fuel.|
|Faulty or clogged fuel cap||The vent in the cap can get clogged causing your tank to form a vacuum restricting fuel flow||Use a thin piece of wire to try to clear the clogged vent. Replace the cap if needed.|
|Bad spark plug||Excessively dirty or broken spark plug; bad connection; not gapped correctly||Replace with a new spark plug, secure connections, and ensure it is gapped to manufacturer specifications|
|Plugged air filter||Dirt and grass can plug the air filter preventing airflow||Remove the filter and clean it. Replace the filter if it is in bad condition.|
|Plugged fuel filter||A dirty fuel filter will restrict fuel flow||Replace the fuel filter|
|Bad fuel pump||A failed or leaking fuel pump will no longer create the pressure needed to pump fuel||Replace the fuel pump|
|Blocked fuel lines||Bad fuel deposits and dirt can build up and clog the fuel lines preventing the engine from getting the required fuel||Use a carb cleaner and compressed air to clear the clog out of the fuel line. Replace the line if necessary.|
|Dirty carburetor||The carburetor can become dirty and clogged due to bad fuel and ethanol deposits preventing fuel flow||Clean the components making up the carburetor. Replace if needed.|
|Bad battery or loose & dirty terminals||A dead battery, loose cables, or corroded terminals can cause starting problems||Charge your battery and replace it if it won’t hold a charge. Make sure your cables are tight and clean the corrosion from terminals.|
|Bad safety switch||Safety switches are a safety measure that exists to prevent your mower from starting in certain situations. When a switch fails, your mower may not start.||Test and replace faulty safety switch|
|Bad ignition switch or coil||Your mower will not start when either the ignition switch or coil is bad||Test and replace a bad switch or coil.|
|Broken recoil||A pull start mower may have a damaged or broken recoil preventing the recoil to initiate starting your engine||Check the recoil to see if it can be restrung or if broken parts, like the pulley, can be replaced. Replace the recoil assembly if needed.|
|Bad Starter Solenoid||An ignition switch that hums when turning the key indicates you may have a problem with the starter solenoid causing a starting problem.||Test the starter solenoid and replace it if bad.|
|Bad charging system||A charging system that can’t keep your mower charged and is constantly draining the battery must be repaired to prevent starting problems.||Take your lawn mower to your local lawn mower dealer for assistance identifying which part of the charging system has failed.|
17 Reasons a Lawn Mower Won’t Start
No Fuel in the Fuel Tank Will Cause a Lawn Mower Not to Start
Even though you know a lawn mower requires gas to start, I’m going to mention it anyway. Sometimes when you’re frustrated with your mower you skip over the simple things when diagnosing your problem.
Solution: Fill your gas-powered lawn mower with gasoline that has an octane rating of 87 or higher and an ethanol level no greater than 10%. Read more about choosing the right gas for your lawn mower here.
Bad or Old Fuel Will Cause a Lawn Mower Not to Start
Gas can begin to break down and become less effective as soon as 30 days after you purchase the fuel. The sticky substance left behind by ethanol and moisture in the fuel can begin clogging your fuel system including the fuel lines, fuel filter, and carburetor.
When you are not able to use your fuel within 30 days, you should add a fuel stabilizer. Add this to the gas you run in your fuel tank in addition to any gas remaining in a storage container.
Solution: Remove the old fuel. Flush the tank and add fresh fuel. Add a fuel additive to clean your fuel system and stabilize it. I have had good results using a product called Sea Foam Motor Treatment. You can read more about why I use Sea Foam here.
Bad Fuel Cap Will Cause a Lawn Mower Not to Start
Without a vent in the fuel cap, the tank will act like a vacuum and restrict fuel from flowing through the fuel lines. Old fuel can cause clogging in the vent so air will no longer pass through the cap.
To isolate your cap as being the cause of your lawn mower starting problem, start and run your mower for a while with the cap off and then with it on to see if your cap affects the running ability of your lawn mower.
Solution: You may be able to clean your fuel cap and unclog the vent. If you are unable to remove the clog, replace your cap with a new one.
Bad Spark Plug or Loose Connection Will Cause a Lawn Mower Not to Start
A spark plug may no longer work and cause intermittent starting and running issues with your lawn mower. A spark plug that is dirty from carbon buildup must be cleaned or replaced if the tip appears very dark in color.
A damaged spark plug that has a broke porcelain insulator or burnt electrode must be replaced as well. To minimize the problems you have during the mowing season from a spark plug, it is best to start a season with a new plug. Some lawn mower engines require 2 spark plugs.
Starting problems can also be caused by a spark plug that is incorrectly gapped or has loose spark plug connections.
Solution: Remove your spark plug and inspect it for signs of carbon buildup or cracked porcelain insulators. Replace with a new spark plug(s). Make sure to gap them according to manufacturer specifications and that the spark plug wires are securely attached.
Plugged Air Filter Will Cause a Lawn Mower Not to Start
A lawn mower requires clean air to run. The air filter prevents dirt and debris from entering the air intake and contaminating the engine. Dirt in the engine can cause significant engine damage.
Never run your mower without an air filter even if it’s only for a short period of time while you source a new filter.
When an air filter gets plugged so air is no longer able to pass through the filter, your mower won’t start. It is important to regularly check the air filter and keep it clean. By checking, cleaning, and replacing this inexpensive part when needed, you can prevent an expensive engine repair.
Solution: Carefully remove the air filter from the air filter housing so you don’t allow dirt to fall into the air intake. If you find dirt in the housing, wipe it out with a clean cloth. Follow one of the following procedures for your type of air filter:
Clean a paper lawn mower air filter
- Knock out the excess dirt in the filter by tapping it against a solid surface.
- Hold the filter up to a light source and check for light shining through the paper element.
- Reuse the filter if you can see light pass through the paper. If you cannot, replace your filter with a new air filter.
- Install the air filter and attach the cover.
Clean a foam lawn mower air filter
- Determine whether you can reuse your filter before cleaning it. If your filter has dark spots or is dry and brittle, replace the filter with a new one.
- If your filter is in good condition, proceed with washing it with mild dish soap and water to remove dirt from the filter.
- Rinse the filter and lay it flat to dry. Placing it outdoors in the sun will speed up the process.
- Once the filter is dry or if you are using a new foam filter, add a foam filter oil to lightly saturate the filter. You don’t want it dripping with oil.
- Install the filter into the housing and attach the cover.
Plugged Fuel Filter Will Cause a Lawn Mower Not to Start
The fuel filter’s function is the strain the fuel coming out of the fuel tank to prevent dirt from entering the fuel system and engine. If your fuel filter is plugged and prevents fuel from passing through it, it must be replaced.
Solution: Replace a plugged fuel filter. You will find a small arrow on the side of the filter. The filter must be installed with the arrow pointed in the direction of your fuel flow. The arrow should be pointed toward the carburetor and away from the fuel tank.
Blocked Fuel Line Will Cause a Lawn Mower Not to Start
A lawn mower fuel line can become clogged by dirt and the sticky substance left behind by old gasoline. This keeps fuel from getting to your carburetor and to your engine. Read more about identifying a clogged fuel line here.
Solution: Remove the fuel line, spray carburetor cleaner into the tube and use compressed air to blow air through the tube until the line is free of dirt and gummy residue. Repeat as necessary. Replace the fuel line with a new line when you can’t remove the clog.
Faulty Fuel Pump Will Cause a Lawn Mower Not to Start
A mower uses a fuel pump when the carburetor is placed higher than the fuel tank. The fuel pump is needed to pump fuel from the fuel tank up to the carburetor. The pump can fail over time from old fuel sitting in the pump and deteriorating the pump components.
Solution: To identify a failing fuel pump, first, inspect your vacuum fuel pump for cracks. If you see fuel outside of the fuel pump or cracks in the pump, the pump will no longer be able to create the pressure needed to pump fuel.
Using the fuel shut-off valve, if your mower has a valve, or pinch pliers to stop and start fuel flow will help you control fuel flow. Stop and start flow to make sure you are getting fuel to the pump.
Once you verify your pump is getting fuel, check to make sure that fuel is being pumped out of the pump in a steady or pulsating flow by removing the fuel line from your carburetor and placing it in a container.
Start your mower. The fuel pump is working correctly if a steady or pulsating flow of fuel is coming out of the fuel line. Replace a bad fuel pump.
Dirty Carburetor Will Cause a Lawn Mower Not to Start
Your mower uses a carburetor to regulate the amount of gas mixed with air allowed into the cylinder to form a combustion.
The additives added to fuel, including ethanol, can cause gummy substances to form in your carburetor. The substance clogs the small parts in your carburetor restricting fuel.
Solution: If you are somewhat mechanical, you can try to clean the carburetor on your lawn mower. If you are not, have a local lawn mower repair shop perform the work. You can find steps for cleaning your carburetor in this article.
You may choose to replace the carburetor if it appears to be in very bad condition. Have a small engine repair shop clean the carburetor if you don’t want to attempt the cleaning or rebuilding the carburetor.
Bad Battery or Loose Terminals Will Cause a Lawn Mower Not to Start
All lawn mowers, other than recoil manual start push mowers, require a battery to start. Make sure your cables and battery terminals are secure.
Clean any corrosion you find on your terminals using a baking soda solution (2 cups water to 3 heaping tablespoons of baking soda). Once you confirm you have a good connection, continue testing the battery.
Solution: Test your battery with a multimeter. You want a reading at about 12.7 volts for 12-volt batteries. Charge your battery if it is lower than this level.
You can find more information on charging your battery here. A battery that is dead or won’t hold a charge must be replaced.
Bad Ignition Switch Will Cause a Lawn Mower Not to Start
Your lawn may have an ignition switch that has failed. If you turn the key in your ignition switch and nothing happens or it just doesn’t feel right, you need to check your switch using a multimeter.
Solution: Replace the ignition switch if bad
Bad Ignition Coil Will Cause a Lawn Mower Not to Start
First, confirm you have a good spark plug. The ignition coil provides voltage to the spark plug so it can fire and start the engine. The engine will not start if the spark plug isn’t able to fire. Next, check the continuity of your ignition coil using an ohm meter.
Solution: Replace the ignition coil if you find a break in the continuity.
Bad Recoil Will Cause a Lawn Mower Not to Start
Manual start push mowers utilize a recoil to start the mower. The recoil can break and you are no longer able to start your mower.
Solution: If the rope is no longer wrapped around your recoil, you may be able to restring it to get it working again. You may have a broken pulley, spring, or clips that need to be replaced.
If you find broken parts, you should price out the parts in addition to the whole recoil assembly. It may be more cost-effective to replace your recoil.
Bad Starter Solenoid Will Cause a Lawn Mower Not to Start
A lawn mower solenoid on your lawn mower is an electromagnetic switch that is like an on-off switch that actuates the starter motor to turn over the engine.
A click or hum when turning your ignition key is an indication to check your solenoid. Another indication your lawn mower solenoid may be bad is when a wire attached to your solenoid gets hot and begins to smoke or melt.
Solution: Test your lawn mower solenoid by following the steps here. Replace your solenoid if it is found to be bad.
Bad Safety Switch Will Cause a Lawn Mower Not to Start
Your lawn mower may use several safety switches in its operator’s presence control system. The switches are designed to kill the engine when the operator leaves the seat and the mower deck is engaged.
A faulty switch may not recognize when the operator is in or out of the seat causing your mower not to start.
Refer to your operator’s manual for the different types of safety switches used in your type of lawn mower.
Solution: You can temporarily bypass the safety switch to identify a bad switch. Do not operate a mower without the safety switch installed for your safety. Always have safety switches installed and working on your equipment. Replace a bad switch.
Faulty Charging System Will Cause a Riding Lawn Mower Not to Start
While the charging system isn’t the main reason a riding lawn mower won’t start, it can contribute to a weak battery that prevents the mower from starting.
When the charging system fails to charge the battery, the battery may not be able to start the mower the next time you go to use it.
A bad stator or alternator can be the problem along with several other electrical parts. Read this article to test your charging system here using an ohm meter.
Solution: I recommend having your lawn mower looked at by a professional lawn mower dealership to identify your charging system. There are so many pricey electrical components that can cause your starting problem.
If you are not experienced with the charging system, you will probably just be throwing parts at your mower hoping it will solve the problem.
This can get very expensive especially when most stores do not allow you to return electrical components if they aren’t the cause of your problem.
Make sure the mechanic is experienced in this area or bring it to your local dealership to be fixed. I have seen, on many occasions, mechanics just throwing parts at mowers, billing the customer, and never fixing the problem.
Many of those customers ended up bringing their mowers to the dealership to be fixed correctly. Most top-brand mowers require their dealerships to have factory-trained mechanics on staff.
Incorrect Operating Procedure Will Cause a Lawn Mower Not to Start
Your lawn mower has safety features that won’t allow your mower to start unless you follow its starting procedures. This may be setting the brake, putting the mower in neutral, and adjusting the choke. Starting procedures vary depending on the type of lawn mower you are using.
Solution: Refer to your lawn mower’s operating manual to ensure you are operating your lawn mower correctly, so you don’t set off the safety features that shut off your lawn mower or don’t allow it to start.
Still Having Problems with Your Lawn Mower?
Lawn mower ownership doesn’t 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!“