Lawn Mower Starts Then Dies – Why?

You’re all set for that smell of freshly cut grass, but when you go to start up your lawn mowers, it gets going – but then dies! What’s up?

If this happens to your lawn mower, this might be why:

Possible Causes

  • Clogged Carburetor
  • Old or Dirty Gas
  • Fuel Cap
  • Fuel Line
  • Spark Plug

Problem and Solution

Engines are complex machines with many moving parts. There are a whole host of issues that could be preventing your lawn mower from running correctly.

If your lawn mower starts then dies, it is most likely due to one of the following issues.

Clogged Carburetor

The carburetor is the component that the gas passes through after exiting the fuel line. It adds the perfect balance of oxygen to the gas for proper combustion in the engine.

If it is clogged, damaged, or dirty, it cannot add oxygen, and the gas will not combust correctly.

To remove the carburetor, start by removing the air filter.

Next, disconnect the fuel line. Do this by pinching the clip on the fuel line and sliding it back. Unbolt the carburetor from the engine and tilt the carburetor to remove the governor and choke rods.

Repairing Lawn Mower Engine

Now that the carburetor is free, open it up to check for debris and build-up. Inspect and clean the carburetor. A carburetor cleaning solution is the best option.

The most likely place for there to be an issue with the carburetor is the carburetor bowl.

If the carburetor is damaged or you cannot clean it, you will need to buy a new one. Depending on the part of the carburetor that is damaged, you may be able to find a replacement part.

Old or Dirty Gas

If you leave gas in the lawn mower for long periods without using it, components of the gas tend to evaporate over time and gum up other processes. If you have not changed the gas in a long time, drain the tank and try running it with new, fresh gas.

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To avoid stale gas from damaging your lawn mower, drain it before winter storage or use a gas stabilizer.

Non-functional Fuel Cap

The fuel cap is the cover over where you put the gas into the lawn mower. If it is not venting correctly, there is not enough air getting into the fuel tank.

It is essential for there to be good airflow because as the tank drains, the space it leaves fills with air. If there is no air to fill it, this will create a vacuum, and the gas will stop flowing.

The easiest way to check if the fuel cap is functioning correctly is to fill the gas tank and attach the cap back securely.

fuel cap on lawn mower

Once you do this, get a bucket ready and disconnect the fuel line from the fuel tank. On most lawn mowers, this is a simple matter of pinching and sliding back the clip so that the pipe is free to be removed.

Once the fuel line is off, the gas will start flowing into the bucket. If the gas begins to slow or stop before the tank is empty, this means the fuel cap is not venting.

Remove the cap to check the gas level inside and notice if more gas comes out when you do.

Now that you are sure the problem results from a non-functional fuel cap, simply replace the cap with a working one.

Damaged or Clogged Fuel Line

If the fuel cap is not the issue, the problem may be further down the line. The fuel line is the pipe that runs from the gas tank to the engine. If it is clogged, the fuel is not getting to the engine, and if it is damaged, it may leak.

In either case, the best way to check the fuel line is to start by removing it. To remove the fuel line, start by pinching the clamp and sliding it back, then pull the line away from the fuel tank.

Move to the other end and repeat the process to remove the line from the carburetor.

Once you have the line free from the mower, inspect the inside to check for blockages. Using a flashlight is a big help. You can also try running water through the tube to check for flow.

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If there is no blockage, inspect the pipe for damage.

To check for unseen holes, plug the ends of the pipe and submerge it in water to check for bubbles. Be sure to let the pipe fully dry before you try to run gas through it again.

If the pipe is blocked, try cleaning it with a gas cleaning solution and a bottle brush. If it does not come clean, or if the tube is damaged, simply replace it.

Broken Spark Plug

The spark plug is a critical component in any engine. If it is not working, there is no spark to ignite the fuel, and therefore, no combustion to run the engine.

To check the spark plug, remove the spark plug wire. Unscrew the spark plug with a spark plug wrench.

You will be able to tell if the spark plug is damaged just by looking. If the porcelain insulator is cracked or the electrode is damaged, you will need a new spark plug.

If you do not see any damage to the spark plug, check its functionality by reconnecting the spark plug wire, ground the metal side of the spark plug, and try to start the mower.

If the spark plug is working, you should be able to see a bright blue spark. If not, then replace it. If the new plug still does not work, there may be an issue with the wiring.


Should I mow wet grass?

Generally speaking, no, mowing wet grass is not a good idea. While most lawn mowers are capable of cutting wet grass, it puts more strain on the mower and will never look as nice as cutting dry grass.

Additionally, wet grass is more likely to clog up the mower and damage parts. You don’t want to get water into your engine parts.

mowing wet grass

How should I maintain my lawn mower?

The best way to keep a lawn mower running well for a long time is to maintain it regularly. You can do this by cleaning it, changing the oil per the manual, and keeping the blades sharp.

Check it over every so often to prevent debris buildup or replace damaged parts before they break.

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How should I put away my lawn mower for winter?

When it comes to fuel, you will want to empty the fuel tank or use a fuel stabilizer before storing the lawn mower for winter.

Additionally, you should change the oil and clean the whole mower. Be sure to store it in a place that will keep it dry so that the blades do not rust and the parts are not damaged by water.

How do I clean a lawn mower?

To clean a lawn mower, start by emptying the gas tank and disconnecting the spark plug wire. Once you have done that, put the mower on its side to clean the bottom.

You can hose down the blades and use a scraper for any stubborn clippings.

Clean the outside housing with a damp cloth and blast the engine parts with compressed air to remove any debris that has made its way inside the housing.

Lastly, reconnect the spark plug, put in new gas, and run the mower for an extended period to flush it out and ensure it is running properly.

woman mowing lawn

What type of gas does my lawn mower use?

For most lawn mowers, you should find the type of gas required listed in the manual or on the fuel cap.

Generally speaking, a four-stroke engine needs a high-quality, unleaded gas with at least an 87 octane rate.

A two-stroke engine requires this to be mixed with two-cycle engine oil in a 50:1 fuel to oil ratio.

Wrapping Up

A broken lawn mower can be frustrating, but more often than not, the issue can be easily resolved. A clogged carburetor is the most common issue people face when their lawn mower starts then dies.

Remember, you may also have a combination of these issues. If your gas is old, the carburetor and fuel line have likely become clogged.

The most essential thing to remember when checking your lawn mower over is to be meticulous. You don’t want to miss something easily fixable.

Furthermore, regular care and maintenance of your lawn mower can extend its life by a great deal and prevent these issues in the future.

Replacement parts can be expensive, and taking your lawn mower in for service is a hassle. If you can fix the problem yourself, why shouldn’t you?

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