Is your lawnmower starting then dying seconds later? This can be frustrating.
It wastes your time trying to fix it and prevents you from tidying up your lawn.
Taking the lawnmower to your local garage for a check will waste even more time. 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 from 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.
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Lawn Mower Starts Then Stops: Common Causes
Your lawnmower just started but ran briefly? 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
The primary function of the carburetor is to mix fuel and air in the right quantities. Subsequently, this mix needs to go through a compression chamber where it burns under high pressure— moving the crankshaft and rotating the blade.
A dirty or clogged carburetor compromises the above process, making your lawnmower start and sputter a few seconds later.
Clogging of the carburetor occurs when you leave fuel in it 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 gas flow.
Go for a branded carburetor cleaner; preferably, an aerosol can efficiently blow out the dirt.
There is a range of options on Amazon that could work out for you.
- Spray nozzle type carb cleaners work at all angles allowing you to use them upside down to eliminate any residues effectively.
- High-pressure aerosol sprays clean your carburetor from the outside without the need to open it. They also remove engine oil and any other dirt outside.
- Solvent cleaners can be easily added to the fuel. They disperse moisture and other dirt from the carburetor.
- Use a nylon brush to clean the hard-to-reach surfaces.
If cleaning doesn’t work, you are better off replacing the entire carburetor.
2. Dirty or Worn-out Spark Plug
You can tell a spark plug is functional by the intense sparks it produces during engine cranking. If there are no sparks, it is broken or defective, and you should replace it.
To be hundred percent sure, remove the spark plug 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 generate intermittent sparks.
A bad spark plug leads to decreased engine fuel efficiency. The missing sparks lead to fuel filling up in the ignition chamber and the production of white smoke.
Fixing the Problem
Most lawn mower manuals recommend using a spark plug for 12 to 24 months before doing a replacement. There is no need for a replacement if you have no problems starting the mower.
However, if your spark plug is acting weird before the elapse of the recommended period, a quick fix would be to clean it up.
Carbon may build up at their tips, rendering the plugs ineffective in delivering an efficient spark in the ignition chamber.
To remove 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, go for a total replacement. However, do check for the correct size while purchasing.
3. A Dirty Air Filter
Another cause for concern is a dirty air filter in your lawnmower.
An efficient air filter prevents your mower from sucking dirt and debris— protecting the pistons, valves, and cylinder walls.
A clogged-up one restricts proper airflow, which 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 particles that quickly find their way in.
How To Fix
Luckily, you can clean the air filter. One way to clean it out is using warm water and soap.
Ensure to leave it outdoors for a while to let it dry. The other option is to clean it with compressed air.
Also, lawn mower manuals recommend replacing the air filter box once every year.
4. Old or Stale Gasoline
Old gasoline stored in your lawnmower for extended periods will cause trouble with the engine. The old gas evaporates pretty quickly— leaving behind a gummy residue.
The residue causes the clogging of the internal parts of the engine. What you have next is restricted gas flow that causes it to start and sputter.
If the gasoline is not more than half the tank, top it with fresh gas. The new gas helps to dilute the impurities causing the clogging.
Should the gasoline be more than half the tank, you want to siphon it and replace it with new gas. It’s also ideal to add a stabilizer to the fresh gasoline.
Stabilizers prevent the clogging of the engine parts for up to two years and speed up the mower. You can buy the stabilizers online or at your local store without spending much.
Be keen on the stabilizer fuel ratio to ensure you are putting in the correct proportions.
5. Blocked Muffler
A muffler is meant to silence or suppress the engine’s noise during operation. One of the reasons your lawn mower starts then dies is because of a blocked muffler.
It could be blocked because of rock, dirt, or excess oil leaking.
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 it is out, remove any residues or debris and deploy a carburetor cleaner to eliminate the remnants.
To do this, allow the cleaner to settle for a while and shake the rear end of the muffler downwards.
Finally, reconnect it to the mower, ensuring that it fits properly.
6. Moisture In The Fuel Line
Water in the fuel line of your lawnmower is a recipe for disaster. 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, 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, and let the tank dry before refilling.
For optimal results, always use high-grade fuel.
7. Blocked Gasoline Cap
The fuel cap is usually fitted with a small hole that allows outside air. Consequently, this pushes the fuel into the carburetor via the fuel line.
A blocked hole prevents air flow— creating a vacuum. Guess what happens next? Not enough gas will flow into the carburetor and subsequently into the combustion chamber— leading to the engine starting and stopping.
Fixing the Problem
Remove the gasoline cap from the fuel tank and inspect it for any blockages.
If you see any of it, 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 mark.
When gasoline gets warm, it expands. Excessive fuel in the fuel tank will result in warm gas escaping through the breather hole.
This is a fire risk you want to avoid.
8. Debris Buildup In The Exterior Part of The Mower
If your lawnmower starts then dies, a potential reason for the behavior could be the engine stalling due to debris building up around the blade.
It makes the engine sputter as it attempts to exert more power. 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. Clean the area thoroughly— taking care not to damage the blade.
9. Excessive Engine Oil
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 it through the sight glass to ensure it’s not beyond the maximum level.
You can remove the excess oil through the oil drain plug— loosen it with a right-sized wrench.
Let it flow into a suitable container until it’s reduced to the maximum level.
We have listed some typical reasons that could cause your lawnmower to start and then die shortly after. We have also shown you how you can go about fixing the problem.
However, prevention is always better than cure. A first good step is reading the manufacturer’s manual to understand the basics of lawn mower maintenance.
Job Kiniale is a certified crop scientist and gardening enthusiast with a passion to help beginning gardeners navigate their newfound hobby. Let’s talk about plants, backyard ideas, and general gardening advice. Outside work, Job loves spending time with family.