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15 Reasons a Self-Propelled Lawn Mower Won’t Start (Solved!)

A lawn mower helps you manage the length of your grass. It not only helps keep the lawn looking well-manicured, but it also prevents bugs and rodents that are attracted to long grass.

So when it won’t start, it’s a top priority to get it running again so you don’t have to deal with the negative effects of an overgrown lawn.

A self-propelled lawn mower that won’t start may be caused by a lack of fuel, a plugged air filter, a clogged fuel line, a plugged fuel filter, a dirty carburetor, a bad spark plug, a bad ignition coil, or a faulty recoil.

Additionally, mowers with an electric start may have problems starting when the battery, ignition switch, or starter solenoid is bad.

Follow the safety precautions listed in your operator’s manual. This includes removing the spark plug prior to performing any repairs.

Self-propelled mower won't start

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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.

Reasons a Self-Propelled Lawn Mower Won’t Start

No Gas in the Fuel Tank

You purchased a gas-powered lawn mower so you’re aware you need gas in order to keep it running. That doesn’t mean you didn’t forget the last time you filled up with gas or notice you developed a fuel leak.

I only mention a lack of fuel being a reason for your lawn mower not starting because it’s an item that may be skipped when checking for a starting problem.

Check the fuel level and look for any fuel leaks. Repair any leaks and fill the fuel tank with fresh fuel.

Fuel Valve is in the Off Position

Some lawn mowers have a valve that shuts off the fuel supply. It is usually located near the bottom of the fuel tank.

If you have a fuel shut-off valve, make sure it is not keeping fuel from flowing through the mower. The fuel supply could have been shut off using this valve while it was being stored, transported or repaired.

Bad or Old Fuel

Fuel can be a big problem when you allow it to sit for extended periods of time before you consume it. Gas can begin to break down and become unstable as soon as 30 days after purchase.

Ethanol in the gas attracts moisture from the air. This moisture and ethanol mixture can leave behind varnish and gummy deposits. This will cause fuel restrictions resulting in a self-propelled mower running sluggish or having trouble starting.

Because of the negative effects old fuel has on your mower, it’s important to consume it within 30 days. If you are unable to use the amount of gas you purchased within this time, add a fuel additive like Sea Foam or STA-BIL to stabilize it to make it last a little longer.

Sea Foam not only stabilizes the fuel, it reduces moisture and cleans the fuel system. You can find more information on using Sea Foam here.

If you find old fuel in your lawn mower, drain the fuel using a fuel siphon pump. Add fresh fuel mixed with a fuel additive like Sea Foam. Use gasoline with a minimum octane rating of 87 and an ethanol content of 10%.

Two-cycle engines require a gas and oil fuel mix and 4-cycle engines require gasoline (not mixed with oil). Read more about choosing the right fuel for your mower here.

Incorrect Operation

Self-propelled mowers have a bail lever or handle for the safety of the operator. This is an item that will immediately stop the engine when the lever is released.

The lever must be pulled back and held against the handlebar to start and run the mower. The mower will not run without the operator present to depress the bail lever.

Make sure the bail lever is held against the handlebar while turning the ignition key on an electric start mower or pulling the recoil on a manual start mower. Only let go of the bail lever when you want to stop the mower.

Clogged Fuel Filter

The fuel filter strains the fuel to prevent dirt from entering the fuel system and your engine causing damage. The fuel filter can become so plugged that fuel isn’t allowed to pass. When you find the filter is plugged, remove it and replace it.

If your mower uses an inline fuel filter that is inserted between the fuel lines, install the new filter with the arrow on the side of your filter pointing in the direction of your fuel flow. The arrow should be pointed toward your carburetor and away from the fuel tank.

Some self-propelled mowers won’t have an inline fuel filter. In that case, you may want to look up a parts diagram for your mower to find if a different style of a fuel filter is being used. Some mowers use a filter or screen located at the bottom of the fuel tank.

Blocked Fuel Line

Dirt and deposits formed from running old fuel can cause a blockage in the fuel line. Check the fuel line by stopping your fuel flow using the fuel shut-off valve. If your self-propelled mower doesn’t have a valve, crimp your fuel line using fuel pinch-off pliers to stop the flow.

Remove the hose from the carburetor and place it in a container. Start your fuel flow and make sure you are getting fuel into the container. The container must be placed lower than the fuel tank. Fuel cannot run uphill without the assistance of a fuel pump.

If you don’t get a good flow of fuel out of the fuel line into the container, stop your fuel flow and remove the fuel line from your mower. Spray carburetor cleaner in the line to loosen up the clog. Use compressed air to blow through the line to remove the blockage.

Repeat using carburetor cleaner and compressed air if needed. If you cannot free the line of the clog, replace it with a new fuel line.

Dirty Carburetor

The carburetor’s function is to regulate the amount of gas mixed with air to form combustion in the cylinder. When the carburetor is dirty and gums up from old fuel, components in the carburetor no longer function properly.

The carburetor may not allow the release of gas required to start your mower.

If you have verified you are getting fuel to the carburetor, remove the air filter and spray carburetor cleaner into the air intake. Start your mower. If it starts, runs, and then shuts down, take your carburetor apart to clean it.

Clogged Air Filter

A plugged air filter can restrict airflow to the mower and not allow the engine to get the air it needs to form combustion. It is best practice to replace your air filter annually. Maintenance doesn’t stop there. You must check and clean your air filter regularly throughout the season.

Clean a Paper Air Filter:

  • Remove the air filter from the filter housing.
  • Wipe dirt and debris from the housing and cover. Be careful to not allow dirt to fall into the air intake.
  • Tap the paper air filter against a solid surface. You’re knocking the dirt loose and allowing it to fall to the ground.
  • Next, hold your filter up to a light source. If you see light shine through the paper, go ahead and continue to use it. If you don’t see light or the filter is very dirty, wet, or damaged, replace it with a new one.
  • Install the filter and reattach the filter cover.

Clean a Paper Air Filter with a Foam Pre-Cleaner:

  • Follow the steps above to clean the paper air filter.
  • To clean the foam pre-cleaner, wash it in a mild detergent and warm water solution.
  • Rinse the filter until the water runs clear.
  • Allow to air dry. (DO NOT add oil to a foam pre-cleaner).
  • Reinstall the paper air filter and foam pre-cleaner.

Clean a Primary Foam Air Filter:
If your self-propelled mower only uses a foam air filter as the primary filter, follow these instructions.

  • Remove the foam air filter from the filter housing.
  • Wipe dirt and debris from the housing and cover. Be careful to not allow dirt to fall into the air intake.
  • Wash the filter in a mild detergent and warm water solution to clean it.
  • Rinse the filter until the water runs clear.
  • Allow to air dry.
  • Add a foam filter oil or motor oil to lightly coat the filter. Squeeze the filter to remove excess oil. You want the filter to be fully covered with the oil, but not dripping with oil.

When you are unsure what type of filter is being used in your mower, refer to the operator’s manual for cleaning instructions.

Bad or Improperly Gapped Spark Plug

A spark plug can be faulty and fouled when the tip is dirty, the porcelain is cracked or the electrode is burnt. You can clean the spark plug to remove the deposits on the tip using a wire brush.

If your spark plug tips are very dark in color or damaged, you must replace your spark plug.

Your spark plugs must be properly gapped following the manufacturer’s specifications as found in your operator’s manual. Starting problems can be caused by a spark plug that is gapped incorrectly or loose spark plug wires.

Bad Ignition Coil

Before checking for a bad ignition coil, make sure your spark plug is in good condition. The ignition coil provides voltage to the spark plug so it can start the engine. If the spark plug isn’t able to fire, the engine will not start.

Check the continuity of the ignition coil using an ohm meter. If you find a break in the continuity, replace the ignition coil.

Bad Recoil

The recoil on your mower may no longer be able to start your mower. A rope on the recoil can become unstrung or you may find you have a broken pulley, springs, or clips in your recoil that need to be repaired.

Sometimes, restringing the recoil is all you need. Other times you will have to replace broken parts in your recoil. Before doing this, price out a full recoil replacement.

Depending on the price difference, it may be better to replace the recoil assembly over tearing it down and replacing broken components.

Bad Fuel Cap

A fuel cap is vented to allow air to pass through the cap. When the vent in the cap becomes clogged, your fuel tank will not be able to vent causing it to form a vacuum restricting fuel from flowing out of the tank.

Run your mower with and without the fuel cap. If it starts without the cap but eventually shuts down after replacing the fuel cap, you may have a cap that cannot vent. Replace it with a new lawn mower fuel cap.

Bad Battery or Blown Fuse

If you use a self-propelled mower with an electric start, the battery may be bad or it might not have a sufficient charge to start your mower. Try to start your mower with the manual recoil. If the mower starts with the recoil, you have a problem with the electric start.

Check the battery. Some mowers have an external charger that plugs into a standard outlet to charge the battery. A battery charger will be used for others.

When the battery fails to charge, check the fuses. If the fuses are fine, replace the battery. If it still doesn’t charge, have your self-propelled mower looked at by an experienced mechanic to troubleshoot additional charging problems.

Bad Ignition Switch on an Electric Start Mower

You may have a bad ignition switch. You can test it and replace it if it is bad.

Bad Starter Solenoid on an Electric Start Mower

The solenoid on a self-propelled mower is an electromagnetic switch that acts like an on-off switch that actuates the starter motor to turn over the engine.

If you hear a click or hum when turning the ignition key or the wires attached to your solenoid get hot and begin to smoke, you need to test the solenoid.

I have listed steps to check your solenoid here. Replace your starter solenoid if you find it to be bad.

Self-Propelled Mower Starting Problems & Solutions (Quick Reference Chart)

Empty Fuel TankFill with fresh fuel. Make sure a fuel leak hasn’t developed.
Fuel Valve in the Wrong PositionTurn on the fuel supply if the fuel shut-off valve has been used previously to shut it off.
Bad or Old FuelDrain the fuel tank if it is older than 30 days. Refill it with fresh fuel mixed with a fuel additive to clean the fuel system and reduce moisture.
Incorrect OperationEnsure the bail lever is engaged when starting the mower.
Plugged Fuel FilterReplace a plugged fuel filter.
Clogged Fuel LineWhen you don’t get a good flow from the fuel line, remove the line. Clean it using carburetor cleaner to loosen the clog and compressed air to remove the clog.
Dirty CarburetorRemove the carburetor to clean it. Replace any damaged parts using a carburetor rebuild kit or replace the carburetor assembly.
Plugged Air FilterClean a dirty air filter. Replace it when it is very dirty, wet or damaged.
Dirty or Damaged Spark PlugClean a dirty spark plug with a wire brush. Replace a spark plug if it is very dark in color, damaged, or has a burnt electrode. The spark plug boot must make a good connection.
Faulty Ignition CoilUse a multimeter to check for a break in continuity. Replace the ignition coil if you find a break.
Bad RecoilRestring and unstrung rope. Fix any broken or missing parts or replace the whole recoil assembly.
Bad Fuel CapReplace the fuel cap if it doesn’t allow air to pass through the cap to allow the fuel tank to vent.
Bad Battery or Loose Connections (Electric Start)Charge the battery, check the fuses, remove corrosion and make sure the connects are making good contact.
Bad Ignition Switch (Electric Start)Test the switch and replace if bad.
Faulty Starter Solenoid (Electric Start)Check the starter solenoid using these procedures. Replace if bad.
Self-Propelled Lawn Mower Starting Problems & Solutions