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Lawn Mower Starts Then Dies: How To Fix

Is your lawnmower starting then dying seconds later? This can be really frustrating.

It wastes your time trying to fix it and also prevents you from tidying up your lawn.

Deciding to take the lawnmower to your local garage for fixing may even waste more time since you may be forced to wait for a couple of days to get it fixed.

So what should you do when you find yourself in such situations? Fix it yourself.

It’s less costly and may save you the time required for repair. Also, walking to and fro a repair shop is an ordeal in itself.

This article outlines the troubleshooting steps you can take to understand the reasons behind your lawnmower starting and stopping. 

Lawn-mower-stalling

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Lawn Mower Starts Then Stops: Common Causes 

Your lawnmower just started but ran briefly? There should be no cause for alarm. The following are the top reasons why this could be happening. 

  • A dirty, clogged, or faulty carburetor 
  • Broken or worn-out spark plugs
  • A dirty air filter 
  • Old or stale gasoline 
  • Blocked Muffler 
  • Moisture in fuel/ fuel line 
  • Blocked gasoline cap
  • Build-up of debris 
  • Excessive oil in the mower engine

Let’s take a deeper dive into each of these problems and see how we can fix them. 

1. A Dirty, Clogged, or Faulty Carburetor 

Clean-carburetor-of-lawn-mower

Source | https://www.yourmechanic.com/

The primary function of the carburetor is to mix fuel and air in the right quantities. Subsequently, the mix of air and fuel needs to go through a compression chamber.

It’s here that gasoline burns under high pressure moving the crankshaft and rotating the blade. A dirty or clogged carburetor compromises the process above, making your lawnmower start and sputter a few seconds later.

Clogging of the carburetor occurs when you leave fuel in the carburetor for long periods. 

Fixing The Problem 

You can fix the problem by cleaning the carburetor. A carb cleaner removes all the dirt and residue, optimizing the flow of gas.

Go for a branded carburetor cleaner, preferably an aerosol can that can blow out the dirt efficiently.

There is a range of options on Amazon that could work out for you.

For example, spray nozzle type carb cleaners work at all angles allowing you to use them upside down to eliminate any residues effectively. Use a nylon brush to clean the hard-to-reach surfaces of the carburetor.

Some lawn mower models give you the option of unscrewing the float bowl bottom part of the carburetor.

Clean the screw and the carburetor hole as well using the carb cleaner. The process above will need you to remove the carburetor from the mower before cleaning it.

However, you could also clean the carburetor without removing it. Go for solvent cleaners that you can easily add to the fuel. The solvent cleaner disperses moisture and other dirt from the carburetor.

High-pressure aerosol sprays are effective in cleaning your carburetor from outside without opening it. It helps remove engine oil and any other dirt outside the carburetor.

If cleaning doesn’t work, you are better off replacing the entire carburetor. 

2. Dirty or Worn-out Spark Plug 

Replacing-spark-plug-of-lawn-mower

Source | https://www.yourmechanic.com/

You can tell a spark plug is functional by the intense sparks it produces during engine cranking. If there are no sparks, that means your spark plug is broken or defective, and you should replace it.

To determine whether your spark plug is defective, remove it from the lawnmower. Reconnect the spark plug to the ignition coil and ground it by attaching its threaded part to the metal surface of the engine.

Make sure to unplug the fuel pump and its supply from the engine. Crank the engine and observe what happens.

You should notice a tiny spark close to the bent electrode and the bottom pin. The spark produced is responsible for igniting the air-fuel mixture in the engine. Without a spark, your engine will not start or may start and stop short.

The latter is likely to occur if the spark plugs are generating intermittent sparks. A bad spark plug leads to decreased engine fuel efficiency. The missing sparks cause more fill-ups of fuel injections, leading to white smoke from the unburned fuel. 

White-smoke-from-mower

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Fixing the Problem 

Most lawn mower manuals recommend using a spark plug for 12 to 24 months before doing a replacement. Rarely do you need to replace the spark plug socket if you have no problems starting the mower.

However, if your spark plug is showing signs of defectiveness before the elapse of the recommended period, a quick fix would be to clean it up.

What causes your spark plugs to be dirty or generally defective is the buildup of carbon at their tips, making the plugs fail to have an efficient spark in the ignition chamber.

Should you notice the carbon buildup, remove the spark plugs from the lawnmower and clean them up using a wire brush. You also want to get rid of any oil deposits that appear at the tip of the plug wires.

If your spark plug is cracked or worn out beyond repair, your next best option would be a replacement. Check for the correct size when getting a new spark plug.

3. A Dirty Air Filter 

Cleaning-air-filter

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Another cause for concern is a dirty air filter in your lawnmower.

Having an air filter for your lawnmower is essential to prevent your mower from sucking dirt and debris, inflicting damage to pistons, valves, and cylinder walls.

Dirty air filters lead to poor airflow that results in your lawnmower dying shortly after starting due to incomplete fuel combustion.

Given the work environment of a lawnmower, it’s bound to accumulate dirt or debris that quickly finds its way into the air filter, which gets clogged. 

How To Fix

Luckily, you can clean the air filter. One way to clean it out is using warm water with soap.

Ensure to leave it outdoors for a while to dry it off. Your other option would be to clean it with compressed air. 

Also, lawn mower manuals recommend replacing the air filter box once every year

4. Old or Stale Gasoline 

Filling-up-gasoline

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Old gasoline stored in your lawnmower for extended periods is bound to cause trouble with your engine starting. The old gas evaporates, taking with it some elements and leaves behind gummy residue.

The residue causes the clogging of the internal parts of your lawnmower engine. What you have next is restricted gas flow that causes your lawn mower engine to start and sputter. 

Quick Fix 

If the gasoline is not more than half the tank, top it with fresh gas. The new gas helps to dilute the impurities that cause the clogging.

Should the gasoline be more than half the tank, you want to siphon it out and replace it with new gas. It’s also ideal to add a stabilizer to the fresh gasoline in both situations.

Stabilizers prevent the clogging of your engine parts for up to two years and speed up your mower as well. You can buy the stabilizers online or at your local store cheaply.

Be keen on the stabilizer fuel ratio to ensure you are putting in the proper proportions. 

5. Blocked Muffler 

Cleaning-Muffler

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A muffler in a lawnmower is meant to silence or suppress the noise it produces when functioning. One of the reasons your lawn mower starts then dies is because of a blocked muffler.

Your muffler could be blocked because of rock, dirt, or the leaking of excess oil. 

Fixing the Problem 

The quickest way to take care of a blocked muffler problem is to clean it.

If you had started the lawnmower already for a couple of minutes, turn it off to allow it to cool.

The muffler is still always too hot to operate with bare hands. Ensure to put on safety eyeglasses and hand gloves as well. Remove the muffler from the engine by turning it in an anticlockwise direction.

Once the muffler is out, remove any residues or debris physically and proceed with a carburetor cleaner to eliminate any remnants. Allow the cleaner to settle for a while and shake the rear end of the muffler downwards to eliminate any remaining debris.

Finally, reconnect it to the mower, ensuring to fit it properly. 

6. Moisture In The Fuel Line 

Lawn-mower-engine-starts-then-stops

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Water in the fuel line of your lawnmower is a recipe for disaster ahead. It causes your lawnmower to stop briefly after starting or stall on the throttle. 

Fixing the Problem 

Inspect the plastic fuel line for any defects and replace it. If your gas has moisture in it, add an additive that gets rid of the dissolved water.

You can purchase the additive online or locally. 

If the moisture level in the gas is substantial, drain it off, let the tank dry before filling it with cleaner fuel. 

To keep your lawnmower optimally functional, always fill it with the required fuel grade.

7. Blocked Gasoline Cap 

Blocked-fuel-cap

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The fuel cap is usually fitted with a small hole that allows the outside flow of air into the fuel tank. Consequently, this enables gas flow from the fuel tank into the fuel line and eventually the carburetor.

A blocked hole prevents the flow of air into the fuel tank, which creates a vacuum. Guess what happens next? Gas will not flow out of the fuel tank resulting in a lack of air-gas mixture in the combustion chamber.

The lawnmower could start or stop or may not run. 

Fixing the Problem

Remove the gasoline cap from the fuel tank and inspect it for any blockages. The breather hole should not be blocked to allow air to pass through. 

Ensure to clean the breather with a small piece of wire or a nozzle cleaner. Also, when adding fuel to the fuel tank, don’t exceed the maximum level fuel mark. When gasoline gets warm, it expands.

Excessive fuel in the fuel tank will lead to the warm gas escaping through other channels such as the breather hole. This is a fire risk you want to avoid in a running engine. 

8. Debris Buildup In The Exterior Part of The Mower 

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If your lawnmower starts then dies, a potential reason for the behavior could be the exterior part of the mower stalling due to debris buildup.

Debris buildup always causes two potential outcomes.

It makes the engine sputter as it attempts to exert more power in rotating the blades. The debris buildup could also dull the blade. 

Fixing the Problem 

Inspect the underside of the lawnmower, especially the area where debris could build up. Remove all kinds of debris, taking care not to damage the blade. 

9. Excessive Oil In The Mower Engine 

Excessive oil in the mower engine could lead to it stalling shortly after starting. 

Fixing the Problem 

Ensure to check the oil level in the engine. At this point, your engine should not be running.

Use a dipstick to locate the oil level. You could also check the oil level through the sight glass to ensure it’s not beyond the maximum level.

Remove the excess oil through the oil drain plug. You will need to loosen the plug with a right-sized wrench.

Your next action step would be to let it flow into a suitable container until it’s reduced to the maximum level.

Wrap Up 

We have listed some typical reasons that could cause your lawnmower to start then die shortly after. We have also shown you how you can go about fixing the problem.

However, prevention is always better than cure. That is, by regularly maintaining your mower, you can altogether prevent the problems from emanating.

A first good step is reading the manufacturer’s manual after purchasing your mower to understand the basics of lawn mower maintenance.

However, should you witness any troubling signs, there is a handy guide at your disposal.

It’s cheaper fixing a mower yourself than buying a new one.

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