Why a Lawn Mower Turns Over But Won’t Start: 9 Causes

Your mower just won’t start, which is frustrating. When should I get a new mower? Use the information below to troubleshoot the issue and attempt to resolve it before taking drastic measures.

When a lawn mower isn’t getting air, spark, or gasoline due to a clogged fuel filter, filthy carburetor, improper choke setting, bad spark plug, plugged fuel filter, clogged fuel line, bad fuel pump, or old gas, it turns over and won’t start.

Before making repairs to your lawn mower, remove the spark plug wire. As detailed in the operator’s manual, adhere to the specific safety considerations for the type of mower you are using.

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Why a Lawn Mower Turns Over But Won’t Start: 9 Causes

On a lawn mower, a stuck choke or an incorrect choke setting

If the choke isn’t engaged when you try to start a cold engine, it will be challenging to do so. The amount of air passing through the carburetor throat is limited by the choke.

This is done to ensure that while the engine is cold, it receives more fuel than air to create a combustion. To ensure that the engine has adequate air to continue running after warming up, the choke lever needs to be moved to the off position.

A heated engine won’t start with the choke engaged, just as a cold engine won’t start without it. To start your lawn mower after it turns over, the choke must be placed correctly.

If the choke is properly adjusted but there are still problems with airflow, examine sure the choke plate is not jammed. To assist with releasing a stuck choke plate, use carburetor cleaning.

Additionally, make sure the choke cable can move easily. To release the links, use a lubricant like Sea Foam Deep Creep or a comparable substance. Choke cable replacement for worn or damaged cables.

Blockage in a lawn mower’s air filter

The air filter may be another airflow obstruction preventing the lawn mower from starting once it turns over. This crucial component is necessary to prevent dirt from getting into the air intake and irreparably harming the engine.

When the air filter isn’t routinely inspected, cleaned, or replaced, dirt and debris can accumulate and hinder the engine from receiving enough air.

I advise replacing the air filter at the beginning of each mowing season and cleaning it multiple times as the season progresses. Naturally, you will need to clean and replace the filter more frequently if you use the mower more frequently than the average homeowner.

The cleaning procedures for popular lawn mower air filters are listed here. You can locate the information in the lawn mower operator’s manual if you’re not sure what kind of filter you have or how to clean it.

In Guide to Lawn Mower Air Filters: Differences & How to Clean Them, you may learn more about air filters.

How to Clean the Air Filter on a Push Mower

Exercise caution when working close to the engine because it can get hot.

  • To stop the engine from starting, turn off the engine and remove the spark plug boot.
  • Remove the thumb screw that typically holds the engine shroud in place.
  • Be careful not to knock any dirt into the intake as you remove the filter. Use a dry towel to wipe away any remaining dirt from the air filter housing.
  • How to Clean a Paper Filter To remove the dirt from the filter, tap it. Place the filter in front of the light. You must change the filter if you notice any portions of it where light does not pass through or if it appears to be damaged.
  • How to Clean a Foam Filter Use dish soap and water to clean the filter. Excess water should be squeezed out of the filter before laying it flat in the sun to dry. Once the filter has dried, lightly grease it with filter oil so that it doesn’t drip with oil. You should change the sponge filter if it is severely dusty or torn.
  • If your mower uses a foam pre-cleaner, it needs to be replaced if it becomes damaged, overly unclean, or dries out and becomes brittle. The pre-cleaner can be washed in warm soapy water, then laid flat in the sun to dry.
  • Change the pre-cleaner and air filter (if your engine uses a pre-cleaner).
  • Put the engine shroud back on.

How to Clean the Paper Air Filter on a Lawn Mower

Exercise caution when working close to the engine because it can get hot.

  • To stop the engine from starting, turn off the engine and remove the spark plug boot.
  • The engine shroud, which is often a cap secured with a few clips or nuts, should be removed.
  • Be careful not to knock any dirt into the intake as you remove the filter. Use a dry towel to wipe away any remaining dirt from the air filter housing. To blow out your air filter, avoid using an air compressor.
  • To remove the dirt from the filter, tap it. Place the filter in front of the light. You must change your air filter if you notice any sections of the filter where light does not pass through, if the filter is damaged, or if it is too dusty.

a lawn mower’s filthy spark plug

Make use of a 3/4″ or 5/8″ socket wrench to remove the spark plug. The size you require depends on the type of engine your lawn mower has. Look at the plug’s condition.

An intermittent or absence of spark, which is necessary for the engine to start and run, might be brought on by a spark plug that is broken or extremely unclean. Search for a burnt electrode, cracked porcelain, or a dark-colored tip when inspecting the spark plug.

Install a new spark plug if any of these conditions are present. Use a wire brush to clean the plug if it’s clean but still in good shape.

Once the gap is accurate, replace the spark plug. The spark plug wire is then firmly attached.

I advise starting each season with a fresh spark plug since a good spark plug is necessary for a lawn mower to operate well.

in an old lawn mower fuel

Gas does not last very long when it is fresh. In fact, it can start to degrade as soon as 30 days after purchase. Varnish and sticky deposits left over from used gas lead to fuel restriction and component failure.

As a result, it’s crucial to buy fresh gas and use it within 30 days. Avoid ethanol-rich petrol at all costs. Use only gas with an octane rating of at least 87 and an ethanol percentage of no more than 10%.

View more here Gas lawn mowers of this kind use this type. I’ll go into more detail regarding the best gas to use with a lawn mower’s 2-cycle or 4-cycle motor.

Use a gasoline siphon pump to drain the fuel tank if you discover that your lawn mower’s fuel tank contains old gas. To assist clean the gasoline system and lessen moisture, fill the tank with fresh fuel and a fuel stabilizer like Sea Foam.

So that the gas and fuel additive may circulate throughout the system, let the lawn mower run. If you’re still having difficulties starting it, keep reading to learn how to troubleshoot other fuel-related issues that might be to blame.

Lawnmower Fuel Filter Clogged

To keep debris out of the fuel system, a fuel filter is used. A typical inline fuel filter for lawn mowers is positioned in-between the fuel lines. Fuel is strained when it exits the fuel tank.

If the fuel filter isn’t changed frequently, it may clog. This could result in the mower turning over and failing to start since a good flow of gasoline won’t be able to get through the filter.

Replace a damaged or outdated gasoline filter with a new one.

Blockage in a Lawn Mower’s Fuel Line

Next, proceed to the carburetor by following the fuel line that exits the fuel tank. Find any kinks that might be preventing the fuel from flowing properly and causing the lawn mower to turn over but not start.

If you don’t discover any kinks, look for a fuel line obstruction. To begin, use the fuel shut-off valve or fuel pinch-off pliers to stop the flow of fuel.

After turning on the gasoline supply, check each portion of the line by removing the end closest to the fuel tank and putting it in a container to see if there is enough flow.

If a fuel line isn’t receiving enough fuel, turn off the fuel supply and take the fuel line out of the lawnmower.

In the line, spray carburetor cleaner. This is done in an effort to clear the obstruction. The clog can then be removed by clearing the line by blowing compressed air through it. Until the clog is gone, keep using compressed air and carburetor cleanser.

Once the obstruction has been cleared, reinstall the gasoline line. If the limitation is not gone or you discover the fuel line is old and starting to crack, replace it with a new one.

Lawnmower Fuel Pump Failure

When the carburetor is placed higher than the gasoline tank, a lawn mower utilizes a fuel pump. Fuel must be moved upward to the carburetor by the pump against the force of gravity.

Vacuum fuel pumps are typically used in lawn mowers. This type of pump delivers fuel to the carburetor by drawing vacuum from the crankcase.

You must replace the gasoline pump if it fractures or stops functioning properly. You can take certain actions to examine the condition of the fuel pump if there are no obvious physical cracks or fuel leaks.

Ensure that gasoline is reaching the pump’s inlet port before testing the pump. (If you aren’t, look for a fuel line or fuel filter obstruction.)

Remove the fuel line from the carburetor and put it in a container once you have made sure that fuel is flowing to the pump. Start your fuel flow and mower to make sure your pump is operating properly.

Fuel should be pulsing or flowing continuously from the fuel line. If not, the fuel pump has to be replaced.

Find out the pressure with a fuel pressure gauge if your mower has an electronic fuel injection pump. For details on recommended fuel pressure, consult your operator’s manual. If the pressures are lower than what the engine manufacturer specifies as acceptable, replace the fuel pump.

a lawn mower’s filthy carburetor

The carburetor’s job is to combine gas and air so that they can burn in the engine. The carburetor is responsible for starting your lawn mower.

Old gas is much too frequently the major cause of a carburetor not working properly. A varnish left over from used fuel might clog the fuel jet or make internal parts stick.

If the carburetor stops operating, you should try cleaning it, replacing any broken parts, or buying a new one.

Do the following steps before disassembling the carburetor on your lawn mower:

  • Verify that the fuel is flowing properly to the carburetor.
  • Take the air filter off.

Blockage in the Lawn Mower Gas Cap’s Fuel Vent

To bring the air pressure inside the gasoline tank to atmospheric pressure, the tank must be vented. The vent is found in the gas cap of a lawnmower.

The gasoline tank creates a vacuum when the vent clogs and is unable to let air through the cap. Gas cannot enter the carburetor because of this vacuum. Due to a lack of gas, the lawnmower will turn over but not start.

Loosen the gas cap and make an attempt to start the mower to see if that fixes the issue. The gas cap can be the reason why it doesn’t start.

Continue letting the mower run while tightening the cap to further demonstrate that it is the cap that is the issue. Replace the cap with a new one if it starts to sputter, shuts down, and won’t restart unless you loosen the cap.