When you own a lawn mower long enough, you will run into times when it doesn’t start. Finding the starting problem can be frustrating.
A push mower won’t start when the mower doesn’t get the fuel, air, and spark it requires to start.
This may be caused by bad fuel, a plugged air filter, clogged fuel lines, a dirty carburetor, a bad spark plug, a broken recoil, a bad battery, or a bad switch.
It’s important to stay up to date with servicing your push mower to keep it running at its best and minimize starting problems. Keep reading and I’ll share steps to diagnose and repair your starting problem.
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Follow all safety instructions provided in your equipment operator’s manual before 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.
Troubleshoot: Push Mower Won’t Start
If you haven’t completed a routine service lately and changed out the maintenance parts including the fuel filter, air filter, and spark plug, I recommend you do so to ensure they are not contributing to your starting problem.
1. No Gas or the Wrong Gas Affects Starting
Begin with the most obvious problem: fuel. If you don’t have gas in your push mower, your gas-powered mower will not work.
Most push mowers today use a 4-cycle engine that requires unleaded gasoline with an octane rating of 87 or greater and an ethanol level of 10 percent or less.
An older push mower may use a 2-cycle engine which requires an oil and fuel mixture to run your mower. Many gas caps indicate if you are to use an oil and gas mixture.
You can also refer to your owner’s manual to determine what type of mower fuel to use in your older equipment.
Never run straight gas through a 2-cycle engine requiring an oil and fuel mix. If you do, you will most likely have to replace your engine. Using fuel with a 10% or lower ethanol content is required for these types of engines as well.
SOLUTION: Fill your gas tank with fresh unleaded gasoline using an 87 octane or greater. Choose a gas with an ethanol level no greater than 10%.
When your push mower uses a 2-cycle engine, you will want to mix fuel with engine oil designed for 2-cycle engines at the mix ratio recommended by the manufacturer.
To find more information on the fuel to use in your push mower check out This is the Gas to Use in a Push Mower (Don’t Get it Wrong).
2. Choke Lever is the in the Wrong Position or the Choke is Stuck
Your mower uses the choke to restrict airflow so the fuel mixture runs rich in order to start a cold engine.
Once the engine warms, the choke is adjusted to the off position so the airflow is no longer restricted. When this change isn’t made, the mower will quit running.
If you are attempting to start the mower with a warm engine, the mower will not start with the choke engaged. The choke must be off.
SOLUTION: Check the placement of the choke lever. The choke must be ON/CLOSED for a cold engine and OFF/OPEN for a warm engine.
If the choke lever is in the correct position, make sure the choke plate is not stuck. Note: Some push mowers use automatic chokes in place of a choke lever.
3. Bad or Old Fuel
Gasoline begins to break down and lose its effectiveness after 30 days. Ethanol in your fuel will begin to separate from the gasoline and sink to the bottom of the fuel tank along with the moisture it attracts.
The ethanol and moisture combination, once it evaporates, leaves a gummy residue that can cause clogging in the fuel system.
Clogging prevents fuel from getting to the engine and your lawn mower won’t start.
Because fuel begins to degrade relatively quickly, it is best to purchase fresh fuel and consume it within 30 days.
If you have more than a 30-day supply on hand, you need to stabilize it with a fuel additive like Sea Foam Motor Treatment. I explain more about the advantages of using Sea Foam in this article and why this is the fuel additive I use.
SOLUTION: Remove the old fuel in your lawn mower and add fresh fuel.
4. Faulty Fuel Cap
Fuel caps have a vent to allow air to pass through the cap. If the vent on your push mower’s cap is plugged, your gas tank forms a vacuum that prevents your mower from allowing gas to leave the tank.
SOLUTION: Replace your push mower’s gas cap if you are unable to clean the cap and open the vent.
5. Bad Spark Plug or Loose Connection
When your spark plug has a loose connection or it is not properly gapped, your lawn mower’s engine can misfire or fail to start. A plug that is fouled with carbon buildup or oil can result in starting problems.
SOLUTION: Remove your spark plug and inspect it for signs of carbon buildup or cracked porcelain insulator. Replace with a new spark plug if you find it is damaged or unable to be sufficiently cleaned.
Check the connections on your spark plug and make sure it is gapped according to the manufacturer’s specifications.
6. Plugged Air Filter
A push mower uses a thin, rectangular-shaped, air filter. It will typically be a paper or foam air filter. The function of your air filter is to prevent dirt and debris from entering the air intake and damaging your engine.
Your lawn mower needs air to run. When the source of air is blocked, your engine is starved of air and will lose power or not start.
Running plugged air filter not only can cause your lawn mower not to start and run, but it may also cause extensive internal engine damage. This could mean having to purchase a new push mower.
SOLUTION: Take time to inspect your air filter regularly. Clean and replace when necessary. To access your air filter, unscrew the thumbscrews to remove the cover on your air filter housing.
Remove your filter. Be careful to not knock dirt into the air intake when you remove your filter. Wipe out any dirt with a clean dry cloth.
Steps to Clean a Push Mower Paper Air Filter
- Tap your paper air filter against a solid surface to knock as much dirt out of the air filter as you can remove.
- Hold your paper filter up to a light source and look to see if you can see light shine through the element.
- Reuse a filter when you can see light.
- Replace the filter with a new one when you can’t see any light, the filter is extremely dirty or it is covered in oil.
- Install and reattach the air filter cover.
Steps to Clean a Push Mower Foam Filter
- Wash your foam filter with water and mild dish soap to remove dirt and oil.
- Rinse with water until the soap is removed.
- Lay flat and allow to dry. Placing the filter outdoors in the sun will speed up the drying process.
- Once dry, lightly coat with filter oil.
- If you find your foam filter is brittle, has brown spots, or has been torn, it’s time to replace it with a new filter.
- Install and reattach the air filter cover.
7. Plugged Fuel Filter
A fuel filter is used to strain the fuel as it comes out of the fuel tank. When it isn’t changed regularly, it can become plugged restricting the amount of fuel flowing through the filter and through the fuel lines.
Most fuel filters on push mowers are inline filters placed in between the fuel lines. Check the fuel filter on your lawn mower to make sure it is not clogged. Some push mowers may have a filter attached to the fuel tank.
I recommend replacing your fuel filter once a year. You may have to change it more often if you find you added dirty fuel to your mower or if you use your push mower more than the average homeowner.
SOLUTION: Replace a dirty fuel filter. Make sure the filter is installed correctly. There is an arrow on an inline fuel filter to show the direction fuel is to flow through the filter.
8. Clogged Fuel Line
Old fuel and dirt leave deposits that can clog your push mower’s fuel line.
SOLUTION: Remove the clogged fuel line from the lawn mower, spray carb cleaner into the tube, and use compressed air to blow air through the tube until the line is free of dirt and gummy residue. Replace the fuel line when you notice the line is dry and forming cracks.
9. Clogged & Dirty Carburetor
The function of the carburetor is to regulate the right amount of gas with the right amount of air so your engine can create combustion.
Carburetors can get crusty buildup and gummy deposits from using old fuel containing ethanol. When the carburetor is not able to regulate fuel in your push mower, your engine will run rough or it may not even start at all.
SOLUTION: If you are somewhat mechanical, you can try to clean the carburetor yourself, otherwise, bring it to your lawn mower repair shop. You can find steps for cleaning your carburetor in this article.
10. Bad Ignition Coil
The ignition coil sparks the spark plug to start the engine. When the coil is bad, your lawn mower won’t start. It can also be the reason your push mower starts and then dies after it gets hot.
SOLUTION: After you have checked your spark plug is working, check the continuity of your ignition coil using a multimeter. Replace the ignition coil if you find a break in the continuity.
11. Bad Battery or Charger (Electric Start)
If you have an electric start mower, you will have a small battery in your push mower that provides power to the electric starter. Charge your battery using a charger plugged into the outlet on your wall.
Some batteries must be removed to be charged, while others have an outlet that plugs into the wall.
SOLUTION: Replace your battery and/or charger when your battery won’t charge or it fails to hold a charge.
12. Blown Fuse (Electric Start)
Check the fuse on your push mower. The fuse is used to protect your electrical system.
SOLUTION: When the fuse is blown, replace the fuse with the same amperage. If you continue to blow a fuse, have your local lawn mower repair shop troubleshoot the root cause of the problem.
13. Bad Mower Recoil or Starter Rope (Manual Start)
A pull-start type of push mower may not start when the mower recoil is broken.
SOLUTION: A broke recoil may be resolved by restringing the starter rope on the recoil. It may have broken clips, a pulley, or a spring that need to be replaced. Sometimes, it’s most cost-effective to replace the whole recoil assembly than try to repair it.
14. Bad Safety Switch on a Lawn Mower
Your lawn mower uses safety switches in its operator’s presence control system. The switch is designed to kill the engine when the operator lets go of the safety bar (bail lever) on the push mower.
A faulty switch may not sense the operator is present and fail to start.
SOLUTION: You can temporarily bypass the safety switch to identify a bad switch. Do not operate a lawn mower without the safety switch installed for your safety. Replace a bad switch.
Still Having Problems with Your Push Mower?
Push mower owners encounter many common problems over a mower’s lifespan. Every mower develops issues over its lifespan even when purchasing a top-of-the-line lawn mower.
To help you identify the causes of these problems and how to fix them, I put together this guide to help: Common Push Mower Problems & Solutions.