Lawn Mower Starts then Dies (Why + How to Fix)

Aiden Binnie

Discover troubleshooting tips in our comprehensive guide about "Lawn Mower Starts then Dies." Learn the common causes and effective solutions to keep your mower running smoothly.

Maintaining your lawn mower is essential, especially if you want to keep your lawn in good shape. However, even the most well-maintained lawn mowers can develop problems quickly. One common issue you can experience is when your lawn mower starts up but dies almost immediately. This can be frustrating, making it difficult to finish your lawn mowing job promptly.

Here are some tips on adjusting a lawn mower that starts and then dies immediately after. But first;

Table Of Contents

Why Does a Lawn Mower Start and Then Die?

1. Clogged air filter: Adequate airflow is essential for a lawn mower engine to run efficiently. A clogged air filter can restrict airflow, causing the engine to start but not for long.

2. Blocked fuel line: A blocked fuel line can restrict fuel flow to the carburetor, meaning gasoline and oxygen won’t be mixed to create combustion. If there’s no combustion, your mower engine will start but stall.

3. Old fuel: When gasoline overstays, it evaporates, leaving damaging residues on the fuel tank/container. The residues have particles that choke your mown’s internal engine parts, starting with the carburetor, causing the engine to shut off.

4. Faulty carburetor: A carburetor regulates the mixture of fuel and air needed for combustion, which is critical for the engine to run smoothly. If the carburetor is faulty, the engine will start and die immediately.

5. Overheating: Dirty and clogged mower engine parts largely contribute to an overheating engine. The engine will start and shut down almost immediately to prevent further damage.

How to Fix The Lawn Mower?

Here are easy tips to help you fix your lawn mower that starts and then dies;

1. Check the Fuel System

One common reason why your lawn mower can start up but then die is a fuel system problem. First, ensure that the lawn mower tank has adequate and clean gasoline. This may seem obvious, but forgetting to check the fuel tank before starting the mower is easy. If the tank is empty, fuel it and restart the mower.

2. Examine Your Air Filter

The air filter prevents dirt and dust from entering the engine. It might become clogged over time, limiting airflow into the engine and leading to stalling. In most models, the air filter is located near the carburetor and is fitted in a plastic or metallic case. To access the filter, you must remove the cover by unscrewing it. If the air filter is blocked with debris, replacing it with a new one would be good.

Note: When replacing it, you should choose a filter that is compatible with your lawn mower's model. If the air filter appears in good condition, you should inspect the air filter housing. Wipe away any dirt to ensure that the housing is dirt free. This will help ensure the engine receives the proper air to function correctly.

3. Inspect the Carburetor

The carburetor properly combines air and fuel before transferring it to the engine. If the carburetor is faulty, it can cause issues such as starting problems or stalling. Remove the air filter to locate the carburetor near the engine with a fuel line running. Once you've located the carburetor, look for any signs of damage, cracks, or leaks. If the carburetor appears in good condition, check if it is clogged.

You’ll need a carburetor cleaner to clean it. Remove the carburetor from the engine and spray it with the cleaner, ensuring it gets into all the small openings. Once the carburetor is clean, reattach it to the engine and try starting the mower again. If cleaning the carburetor does not resolve the issue, it may be out of adjustment.

The carburetor has several adjustment screws that support its function. If these screws are not adjusted correctly, you'll need to consult the user manual for directions to make the adjustments. It's important to be careful when adjusting because a small change can significantly impact how the engine runs.

4. Inspect the Spark Plug

The spark plug ignites the engine's fuel; without it, the engine won't run. Remove the spark plug and start inspecting it. If the electrode is worn out, it must be replaced. Additionally, ensure the gap between the electrode and the ground is set correctly.

This gap can be adjusted with a spark plug gap tool. Use a wire brush to clean it if it seems dirty but in excellent condition. This can sometimes remove any buildup that may prevent the spark plug from working properly.

5. Check the Blade and Undercarriage

A clogged blade or undercarriage can also cause your lawn mower to start and shut down. Sometimes, grass and debris can tangle around the blade or undercarriage, causing the mower to stall. To inspect the blade and undercarriage, turn off the mower and disconnect the spark plug. Wipe away any grass caught around the blade or undercarriage. Once everything is clean, reconnect the spark plug and try starting the mower again.

6. Adjust the Idle Speed

The engine's idle speed is its pace when it's not engaged in cutting grass. If the idle speed is too low, the engine will halt as you release the throttle. To adjust the idle speed, find it on the carburetor and spin it clockwise to boost the speed or counterclockwise to lower it. You might need to refer to the user manual if you aren’t conversant with the mower’s model.

7. Check the Flywheel Key

The flywheel key is a tiny metal component that links the flywheel to the engine's crankshaft. If the flywheel key is damaged, it can throw off the engine's timing, causing it to start but die almost immediately. To check the flywheel key, remove the engine cover, then inspect the flywheel key for any signs of damage or wear. If it's damaged, it needs to be replaced.


When working on your landscape, a lawn mower that starts well but dies almost immediately can be frustrating. It is critical to determine the source of the problem, such as a clogged air filter, blocked fuel line, old fuel, a faulty carburetor, or overheating. If you encounter these issues, you can fix them by checking the fuel system, the air filter, the carburetor, the spark plug, the blade and undercarriage, the idle speed, and the flywheel. If none of the solutions are working, contact a certified technician!

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