Why Is My Lawn Mower Turning Over But Not Starting

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Ready to get some mowing done but your mower is not starting? It can be quite frustrating if the lawn mower is turning over but won’t start. This can be caused by stale fuel or a dirty air filter.

In this article, I talk about simple DIY troubleshooting tips to help you diagnose the issues and get your mower running again.

Why Is My Lawn Mower Turning Over But Not Starting?

The reasons your lawn mower turns over but does not start may include:

  • Worn spark plugs 
  • Dirty air filter
  • Stale fuel 
  • Clogged fuel filter/fuel line
  • Dirty carburetor
  • Faulty safety switch

Tools You Need For This Job

Some tools you may need for this job include:

  • Work gloves
  • Screwdriver
  • Pliers
  • Multimeter
  • Wire brush
  • Siphon
  • Empty container 
  • Clean rag

Lawn Mower Turns Over But Won’t Start: Causes, Diagnosis, and Fixes

1. Worn Spark Plug

The primary reason for a lawn mower that turns over but won’t start is a worn spark plug.

The spark plug produces the spark that ignites the fuel mixture of the engine, enabling it to start and power the mower.

If the spark plug becomes bad, oil-stained, or covered with carbon build-up it may produce an insufficient spark and the mower will refuse to start as a result.

Also, make sure that the spark plug wire is securely connected to the plug. A shaky contact will weaken the sparks sent to the engine and may as well make your lawn mower turn over but refuse to start.

Diagnosis:

Remove the spark plug wire and take out the spark plug. If the spark plug is oil stained, cracked, or coated in carbon residue, it is worn.

Fix:

Replace the worn spark plug with a new one.

If the plug wire is loose, connect it securely to the spark plug so that it is tight and not wobbly.

2. Dirty Air Filter

A lawn mower that turns over but won’t start may be due to a dirty air filter that has become clogged and is unable to allow air into the engine.

Air is needed by the carburetor to efficiently produce the fuel-air mixture that is sent to the combustion chamber and is then used to run the engine.

When the air is insufficient as a result of a clogged/dirty air filter, the lawn mower may crank or turn over, but won’t start.

Diagnosis:

Turn off the mower and allow it to cool. Then, take off the air filter housing and inspect the air filter. If it is dirty or covered in dust and debris, it is clogged.

Fix:

A paper filter should be replaced with a new one. A foam filter can also be replaced or washed and reused after it has been allowed to dry.

3. Stale Fuel

If you have corrected the spark plug and air filter problem, and the mower still won’t start, the problem might be with the fuel.

Fuel that has stayed in the tank for over 25 days has become stale and may begin to form a sticky residue.

This sticky residue can clog the fuel tank outlet and other fuel delivery systems of the engine, causing the mower to refuse to start.

Diagnosis:

If you have left fuel in your mower for more than 25 days, drain the fuel into a fuel can or any clean empty container, using a siphon.

Allow the fuel to settle. The presence of slimy or sticky residue indicates that the fuel is stale.

Fix:

Drain out all the old fuel and clean the fuel tank and its outlet. Then, pour fresh fuel into the tank.

To prolong the life of the gas and avoid future buildup, fill the tank with fresh fuel and a fuel stabilizer.

4. Clogged Fuel Filter/Fuel Lines

Stale fuel that was used to run the mower will clog the fuel lines and may even clog the filter.

If this happens, fuel delivery to the carburetor will be delayed or stopped completely. 

The engine will be unable to access the fuel that makes it start. This may be the reason your mower turns over but won’t start. 

Diagnosis:

Remove the end of the fuel line at the carburetor and check the rate of fuel flow. If the fuel is dripping slowly or not flowing at all, the fuel filter might be clogged.

Remove the fuel filter using your pliers. Turn it to each side and check the fuel flow. If it is slow or the clear fuel filter container is dirty, it is clogged.

Fix:

Replace clogged fuel lines and filter with new parts.

5. Clogged Carburetor

A clogged carburetor may also be the culprit if your lawn mower turns over but won’t start.

The carburetor jets may get clogged with the residue from stale fuel, making them unable to transport fuel to the engine.   

Also, the diaphragm and the gasket may become worn or damaged. This can as well cause fuel delivery issues from the carburetor to the engine of your mower.

Diagnosis:

Remove the carburetor from the mower using a screwdriver. Inspect the jets, bowl, diaphragm, and gasket for clogging, damage, and any signs of wear.

Fix:

First, use a carburetor cleaner to clean the entire carburetor. To make this cleaning more effective, you can take the carburetor apart before cleaning.

Blast compressed air through the jets and holes to remove any remaining particles.

Then, check the diaphragm, gasket, float needle valve, and other vital parts of the carburetor and replace any worn-out parts. 

6. Faulty Safety Switch

The safety switch of the mower acts as a kill switch. It shuts down the mower or prevents it from starting whenever it detects a problem.

The safety switch sends signals to the ignition system to shut down the engine when it detects a problem. It can send a wrong signal if it gets faulty. 

This is usually the case if the engine turns over but won’t start or if the cranks briefly but then shuts down.

Diagnosis:

Use a multimeter to perform a safety switch test continuity test.

One side should produce a circuit and the other side of the switch should be grounded.

How To Perform A Safety Switch Continuity Test

  • Change the multimeter to the continuity setting
  • Put the two multimeter leads on each spade on one side of the switch
  • Do this for the other side of the switch
  • You should hear a beep (meaning that a circuit has been completed) on one side when the switch button is pushed in
  • The other side should produce a beep without pushing the button

Fix:

Disconnect the safety switch temporarily to allow the mower to start.

Then, repair the wiring or replace the switch if necessary. 

Conclusion

Your lawn mower may turn over but refuse to start as a result of a worn spark plug, stale fuel, clogged fuel filter, blocked fuel line, clogged carburetor, or a damaged safety switch.

These problems are usually easy to detect and fix. Take some time to inspect the various parts and apply the recommended fixes stated in this article to get your mower running again.