Lawn Mower Won’t Start

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Ready to mow but your lawn mower won’t start? Read this article to the end to learn about some practical fixes to get your lawn mower to start so that you can mow without issues.

Some of the common reasons a lawn mower won’t start include:

  • Dirty Carburetor
  • Clogged air filter
  • Clogged fuel filter
  • Faulty fuel cap
  • Bad or old gasoline

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Lawn Mower Won’t Start: Causes And Fixes

1.  Insufficient Gas in the Tank

One of the main reasons why your lawn mower may fail to start is if there is insufficient gas in the tank. 

It is important to always have enough fuel in the gas tank before starting the mower.

In case it runs out of gas and the mowing machine does not start, you do not need to worry because it can be easily fixed.

Fix: Fill the mower with fresh fuel.

2. Bad or Old Gasoline

Using a gas that is either old or contaminated with excess moisture may make the mower not start. 

Over time, some of the ingredients in the gas may evaporate and leave a sticky substance that may clog the fuel system.

Fix: Drain the old gas, flush the tank and add fresh gas. Ensure that you use a fuel additive to stabilize and clean the gas.

3. Loose Connection or Defective Spark Plug

A defective spark plug can make the mower not start. This issue can also occur if the spark plug has loose connections or it is incorrectly gapped.

Fix: Replace broken or dirty spark plug with a new one.

Ensure that you gap the spark plug according to the manufacturer’s specification and secure connections.

4. Clogged Fuel Filter

The mower’s fuel filter can prevent dirt and debris from entering the engine. A clogged fuel filter may cause the engine to misfire, fail to start, and stall when accelerating. 

Fix: Replace the fuel filter

5. Riding Mower Won’t Start Due To Faulty Fuel Cap

This is one of the reasons why your mower may fail to start. There will be a restriction on fuel from flowing through the fuel lines if the fuel cap is without a vent.

Old gas can also clog the vent, not allowing air to go through the cap.  

Fix: Clean the fuel cap to clear out the clog in the vent. You may need to replace the fuel cap if you are unable to remove the clog.

6. Clogged Fuel Line

The dirt and sticky substance left behind by old gas may block the fuel lines. 

This will prevent gas from getting to the carburetor and engine.

Fix: Clear out the clog of the fuel line by using a carb cleaner and compressed air. You can also replace it if necessary.

7. Zero-Turn Mower Won’t Start Due To Bad Fuel Pump

Your fuel pump can malfunction due to old gas that deteriorates pump components. 

In this case, it will no longer create the pressure that is needed to pump the fuel.

Fix: Check the vacuum fuel pump for cracks. If there are cracks in the pump or there is fuel outside the pump, it will be unable to create the required pressure to pump gas.

Use pinch pliers or a fuel shut-off valve to control fuel flow.  Ensure that you stop and start flow to get gas to the pump.

If you notice that it is getting gas, inspect to verify if the gas is pumped out properly.

You can do this by removing the fuel line from the carburetor and placing it on the container and starting the mowing machine.

If there is a steady fuel flow that comes out from the fuel line, it means that the fuel pump is functioning properly. If not, replace the faulty fuel pump with a new one.

8. Bad Battery or Loose Terminals

All mowing machines except for recoil manual start push lawn mowers need a battery to start. 

Ensure that the mower battery terminals and cables are secure. Use a baking soda solution to clean corrosions that you locate on the terminal.

Fix: Test the battery with a multimeter. Ensure that you get a reading of around 12.7 volts. If it is below this level, it’s best to charge the battery. You should also replace the battery if it is dead.

9. Bad Ignition Coil

The ignition coil is responsible for transferring voltage from the battery to the spark plug. Your mowing machine may fail to start if this component is bad.

If you notice this, use an ohmmeter to check the continuity of the ignition coil

Fix: Test and replace the bad ignition coil

10. Walk-Behind Mower Won’t Start Due to Blocked Air Filter

The air filter keeps dust and other particles from entering the engine. 

If the air filter gets clogged, air won’t be unable to go through the filter, causing your lawn mower not to start.

Fix: Remove the air filter and clean it. Replace it if it is in a bad condition.

11. Bad Recoil

Manual start push lawn mowers make use of recoil to start. If it breaks, your mower may develop starting issues. 

This problem may also come from a broken pulley, spring or clips

Fix: Check to see if you can re-string it. In addition, replace the broken spring, pulley or clips.

12. Incorrect Operating Procedure

Your mower may come with safety features that may not allow it to start unless you follow their starting procedures.

This may be setting the brake, putting the lawn mower in neutral, or adjusting the choke. Starting procedures depends on the type of mowing machine that you use.

Fix: Check the mower’s manual to verify if you’re using it properly so that you do not set off safety systems that will shut it down or prevent the mower from starting.

13. Riding Mower Won’t Start Due To Dirty Carburetor

A dirty carburetor may also make your mower develop starting issues. 

Fuel additives may cause sticky substances to form in the carburetor, clogging the small components in the carburetor to restrict gas.

Fix: Replace the carburetor if it is in a bad condition   

14. Defective Starter Solenoid

The starter solenoid is a small magnetic device located inside the starter motor. It closes when you turn the ignition key, enabling electricity to flow to the starter.

You need to inspect the solenoid if you notice a hum or click when turning the ignition key. 

Another indication of a defective starter solenoid is if the cable attached to the solenoid becomes hot and starts to melt or smoke.

Fix: Replace the solenoid if it is in a bad condition

15. Bad Charging System

A bad charging system on the mower will drain the battery and not keep it charged, making the mower not start. This issue may come from a bad stator or alternator. 

This issue must be repaired to prevent starting problems.

Fix: Contact an experienced technician or take the mowing machine to your local dealership to get it fixed.

16. Zero-Turn Mower Won’t Start Due To Dysfunctional Safety Switch

Safety switches monitor the pressure on the seat and can shut off power to the blades if it senses that the seat is unoccupied. 

When the safety switch fails, it may cause the mowing machine to develop starting issues.

Fix: Replace the faulty safety switch.

Note: Do not operate your lawn mower without installing a safety switch.

17. Bad Ignition Switch

A bad ignition switch may make your lawn mower not start.

 It is important to get a multimeter to test it if you turn the key in your ignition switch and nothing happens.

Fix: Replace the ignition switch if it is in a bad condition

18. Broken Flywheel Key

The flywheel key is a small metal that fits into the crankshaft and engages with the flywheel. 

The engine of your mower may suddenly stop if the mower blade hits a hard object.

In this case, it breaks to protect parts like the crankshaft from damage. If the flywheel is broken, the mower may develop starting issues. 

Fix: Replace the broken flywheel key.

Lawn Mower Won’t Start After Winter

Here are some of the reasons why your mower won’t start after winter:

Bad Spark Plug

This is one of the reasons why your mower may develop starting issues after winter. 

Make sure that you use a spark plug tester to check if it is defective. If there is no spark, it means that the spark plug is faulty.

Fix: It’s best to replace the spark plug.

Clogged Carburetor

The stale gas in the lawn mower may clog the carburetor and enter the float bowl. This will make the mower develop starting issues after winter.

Fix: Drain the old fuel from the float bowl and use a carburetor cleaner to clean the carburetor. Replace the carburetor if it is in a bad condition

Flat Battery

The battery may lose power because it hasn’t been charged during the winter period.

Fix: Charge the battery and make sure that the terminals are clean. Replace the battery if it does not hold a charge

Old Gas

The gas of your mower may become less effective over time, leaving a gummy substance behind and corroding the fuel components.

Fix: Drain the gas tank and add fresh fuel. Add a fuel additive to the gas to clean and remove moisture from the fuel system.

Lawn Mower Won’t Start After Cleaning The Carburetor

If you notice that your mower does not start after cleaning the carburetor, it may be as a result of the following:

Worn And Broken Carburetor Parts

The carburetor comes with different components such as:

  • Diaphragms and valves
  • Venturi
  • Outlet and inlet port, including jets
  • The metering unit includes a spring, lever, pin, and a needle
  • Seals, screws, nuts, and gaskets

A broken or worn-out metering unit may prevent the mower from starting despite having a clean carburetor. 

Furthermore, corroded venturi and jets won’t function well. You may also have damaged diaphragms or a blocked valve.

Fix: Make sure that the carburetor is properly installed. The screws and nuts should be snugly fastened.

Check the adjustable screws and fastening bolts if the mower has one. 

Air mixture and idle screws are found in many modern lawn mower models. Replace the carburetor if it is corroded.

The Carburetor is Not Sufficiently Primed

The primer bulb creates a vacuum that draws gasoline through the fuel lines and into the carburetor.

The usual practice is to draw adequate gas into the carburetor but this depends on the lawn mower model. 

However, this may not happen if the primer bulb is broken or cracked.

Fix: Replace the cracked or damaged primer bulb.

Dirty Spark Plug

The mower may fail to start if the spark plug is dirty. You may need to test each end of the spark plug for resistance by using a multimeter.

Fix: Use a soft wire brush to clean the carbon buildup or change the spark plug if it is in a bad condition.

Clogged Air Filter

A clogged air filter may make the mower not start despite cleaning the carburetor.

Fix: Replace the bad air filter with a new one

Water in the Tank

If you notice that your mower isn’t starting after cleaning the carburetor, the problem may occur as a result of water in the gas tank especially if you have left the mowing machine exposed for a long time.

The ethanol in the gas can attract moisture which may make the mower not start.

Fix: If you detect that there is water in the tank, drain the gas tank. 

To do this, use a damp sponge or cloth and fix it towards one end of a long screwdriver and soak up the remaining water.

Bad Gas

The gas in your mower may deteriorate if it is stored in the gas tank for an extended period. Many mowing machines come with a carb bowl connected to the fuel line from the gas tank.

This stale gas may cause the carb bowl to get dirty or clog the main jet. 

This makes it necessary to remove bad gas from the carburetor bowl, line, and gas tank.

Fix: Detach the fuel hose from the carburetor and drain the bad gas into a pan. You can also pump the gasoline out of the tank by using a siphon pump.

Carburetor Isn’t Tightly Bolted or Screwed to the Engine

This may stop your mower from starting despite having the carburetor cleaned. It must be properly screwed because the carburetor is supposed to make an ideal seal with the engine.

Fix: Ensure that the carburetor is tightly screwed or bolted.

Conclusion

If you notice that your lawn mower is not starting, the first thing to do is to figure out the causes.

Some of the possible causes are bad spark plug, bad solenoid, bad safety switch and old or bad gas.

Follow the troubleshooting tips to get your mowing machine working again. Call a technician if the problem persists after implementing the tips shared here.

Top Recommended Handy Tools for Troubleshooting & Servicing Your Lawn Mower

Multimeter – This is useful for checking voltage, continuity & current to identify electrical problems in your mowerFilter Wrench – For loosening your mower’s filter.
Carburetor Cleaner – Choke and Throttle Body Cleaner for cleaning clogs & buildup in the fuel system.Blade Balancer–Balances Blades After Sharpening.
Fuel Stabilizer – This stabilizes & cleans your fuel to reduce fuel system buildupBattery Inflator – This helps to ensure your mower tires stay inflated to prevent steering or uneven cutting issues.
Socket & Allen Wrench Set – These tools are needed to service & troubleshoot your mower problemsTachometer– Evaluates your mower’s engine performance and provides accurate data about the status of the engine
12-Volt Battery Charger – This is useful for charging your mower battery.Lawn Mower Blade Sharpener– Adjustable Lawn Mower Blade Sharpener for Right and Left Hand Blades.