There is nothing more frustrating than seeing your lawn mower dying on you when you’re ready to tackle those tall green blades.
There are many reasons why a lawn mower starts then dies, but the good news is that it is easy to address most of the time.
In this guide, we’ll talk about the most common reasons why your mower could be acting weird and how you can fix it.
We will also share with you some tips on how to keep your machine running in tip-top shape.
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Lawn Mower Starts Then Dies: Top Reasons Why
When your lawn mower starts then dies, it may feel like you are alone. In reality, it is a lot more common than you think.
Even the most expensive models have this issue from time to time. Below are the most common reasons behind the false start and how you can fix it:
1. Dirty Carburetor
The most common reason your mower has trouble starting could be a dirty or clogged carburetor.
The carburetor is the component responsible for mixing gas with oxygen to create combustion. It makes sure there is a correct combination of fuel and air going into the engine cylinder.
The combustion then pushes the engine piston downward, rotating the crankshaft and making the lawn mower blade spin.
Other signs of a dirty or clogged carburetor include:
- Muffler emitting black smoke
- Significant increase in the consumption of fuel
- Engine running rough during mowing
How To Fix It
You can keep the carburetor in good condition by always using fresh fuel to fill the gas tank and adding a fuel stabilizer to help maintain fuel quality.
However, if the carburetor becomes clogged, you must clean it.
Before doing so, uninstall the entire carburetor from the lawn mower engine. After that, follow these steps:
Step 1: Disassemble the carburetor.
Ensure that every piece you remove is put back in the same position. Consider taking pictures while you work to avoid confusion during reassembly.
Step 2: Replace any worn-out parts.
Make the necessary repair or replacement should you spot wear and tear on any components, such as the carburetor bowl, needle, gaskets, or pin.
We suggest having spare parts ready before taking the carburetor apart.
Step 3: Clean the carburetor.
Spray carb cleaner throughout the housing and its parts. If you prefer a liquid cleaning solution, pour it into an empty bucket where the carburetor parts can soak.
Then, rinse the carburetor parts with water and blow dry them with compressed air.
Step 4: Reassemble the parts.
The parts must be completely dry before attaching the carburetor to the mower’s engine. If your carburetor is corroded or badly gummed, you must replace it.
2. Faulty Choke
Another reason your lawn mower may have trouble starting has to do with the choke valve. A choke is a metal flap responsible for moderating air flow in the gas-air mixture.
The choke plate restricts the airflow when starting the engine, allowing more fuel to be pushed into the combustion chambers.
The most common problem that happens in the choke valve is flooding.
If the engine successfully starts, leaving it at full choke for even a few seconds can cause too much fuel to enter the combustion chamber.
In turn, this will cause the engine to lock up and stall.
It can take quite a while to drain the fuel out of the chamber to the point when your lawn mower is easy to start again.
In worst-case scenarios, you may need to open up the engine and drain the fuel.
Another common issue is when the choke doesn’t open and close promptly.
If the choke valve sticks or doesn’t move properly, it can induce flooding. In addition, it can prevent you from closing it fully to allow the engine to start properly.
How To Fix It
The conventional solution for a flooded engine is to give the carburetor time to dry. However, you can try these steps to speed up the process:
Step 1: Pull off the spark plug and dry the plug terminals by wiping them with a dry cloth. Alternatively, you can spray alcohol-based starter fluid.
Step 2: Crank the engine several times to draw out air through the carburetor.
Step 3: Replace the plug, shut down the choke, and crank the engine. If it stalls, crank it a few more times until it starts. Remove the air filter of the engine that doesn’t sputter.
Step 4: Spray the filter with fluid, put it back, and then crank the engine. Lubricate the choke shaft and linkage to keep the choke opening and closing correctly.
3. Bad Fuel
Fuel quality is extremely important for the smooth functioning of your lawn mower.
If the gas in your machine has been sitting inactive for a while, chances are the evaporation has created damaging residue.
This residue then clogs the internal parts of your mower, resulting in restricted gas flow. Hence, your machine will not start properly.
How To Fix It
If your lawn mower doesn’t start because of stale gas, you must remove the residue choking the engine. How do you know the gas in your lawn mower has gone bad?
The easiest way to tell is to smell it. Oxidized fuel has a sour and stronger smell than fresh gas. Another way is to drain a sample from the tank. If the gas is dark in color, it’s most likely stale.
If the fuel tank contains less than half of the old gas, you may try adding new gas to dilute the impurities. If it has more than half of the old gas, it’s best to replace it with fresh gasoline.
In both cases, adding a stabilizer or a fuel treatment solution is a good idea because it prevents residue buildup for up to two years.
Lastly, remember to dispose of old fuel properly.
4. Defective Spark Plugs
Spark plugs are the components that ignite the fuel-air mixture inside the engine’s cylinder.
The machine’s engine relies on them to ignite the air-filled fuel that enters the combustion chamber. Without the spark, combustion won’t take place.
If your mower will not start properly, takes longer or requires harder pulls, has a rough idle, lacks power, or needs more refueling than usual, there is likely an issue with the spark plugs.
How To Fix It
If you spot these symptoms in your lawn mower and want to check if they have something to do with the spark plug, you will need to do some mechanical work.
Fortunately, it is one of the easiest maintenance tasks.
To start, disconnect the spark plug wires and the rubber shroud that fits the end of the spark plug. Next, remove the plug using a spark plug socket.
It is important to use the right tool to avoid causing damage or harm to your engine. Then, remove the dirty spark plug.
Inspect the spark plug for damage, such as black carbon buildup on the electrodes or cracked ceramic coating.
In most cases, you will only need to clean the spark plug, especially if the electrodes are still sharp and at full length.
Use a soft wire brush and dry cloth to remove carbon buildup or oil from the surface of the spark plug.
That said, it is best to replace faulty spark plugs if they seem worn out.
Spark plugs are inexpensive, and replacing them regularly is a good preventive maintenance step for your mower.
5. Too Much or Too Little Oil in the Engine
Oil is important for maintaining engine efficiency. However, too little or too much can create havoc on your equipment.
When there is too much oil in the engine, it creates smoke that causes it to pull air and oil from the engine crankcase and cause the air filter to become clogged.
Consequently, the lack of air can cause your equipment to shut down.
In addition, too much oil can damage the combustion chamber, seals, and gaskets. In worse cases, your engine may even catch on fire.
When there is not enough oil to lubricate the engine’s internal components, friction will begin to create heat. Overheating can cause your lawn mower to shut down.
How To Fix It
If there is excess oil in your lawn mower, you first need to wipe down the excess lubricant using a paper towel, a clean rag, or a turkey baster.
You can also use a vacuum cleaner or drain oil plug to remove surplus oil from the surrounding area.
Next, drain all the oil from the mower by tilting the machine on its side with the carburetor facing upward. Using a gas and oil siphon can save you a lot of time draining the fuel.
Lastly, remove the oil cap or dipstick until all the remaining oil is released. You can add fresh oil to the crankcase if your machine shuts down due to a low oil level.
However, most of the time, when a mower has trouble starting due to lack of lubrication, it’s an indication that the engine has been severely damaged.
In that case, you may need to bring your equipment to a lawn mower repair shop.
To avoid overfilling your mower’s engine with oil, follow the recommendations you’ll find in the machine’s user manual.
Make sure you use the right type and oil viscosity for your mower to prevent engine damage and extend its lifespan.
Moreover, you must avoid spilling oil when filling up your mower. Always check the oil level and fuel lines after each use to ensure it is not too high or too low.
Lastly, keep your engine clean with an engine degreaser. This helps prevent excess engine oil and promotes outstanding engine function.
When All Else Fails
Any of these five reasons could be causing your lawn mower to shut down when you try to start it. Fortunately, fixing these issues is easy with just a few tools and supplies.
If you have tried all the fixes we suggested but still have problems starting your equipment, it could be due to a more serious underlying issue.
In that case, it is best to consult a professional engine mechanic to get it back on track in no time.