9 Reasons a Push Mower Won’t Stay Running

It’s frustrating when your push mower keeps shutting down. You may be able to get it started again, but it just won’t stay running so you’re not able to finish mowing the lawn.

A push mower may not stay running due to a plugged fuel filter, clogged fuel line, dirty carburetor, plugged air filter, incorrect choke setting, bad spark plug, faulty ignition coil, bad gas cap, incorrect engine oil level, plugged mower deck, or old gas.

Before performing repairs, follow the safety precautions found in the operator’s manual. This includes disconnecting the spark plug wire and waiting for all parts to stop moving.

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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

This is Why a Push Mower Won’t Stay Running

Bad or Old Gas

One of the big reasons a push mower will quit and not stay running is old gas. This is because gas breaks down over time while it sits in your mower.

It doesn’t take long for gas to begin to degrade. It can start happening as soon as 30 days after you purchase it.

Because gas contains ethanol, it attracts moisture to the fuel system creating varnish and gummy deposits in the system. These items can cause clogs in the fuel system that restricts the amount of gas to the engine. It can also cause fuel component failure.

To reduce the negative effects of gas, follow these important tips:

• Purchase only the amount of fresh gas that can be consumed within 30 days.
• Always use gas with a minimum 87 octane rating and a maximum of 10% ethanol content.
• For push mowers with two-cycle engines, mix gas with high-quality 2-cycle engine oil.
• If you have more fuel on hand than you are able to consume within 30 days, use a fuel additive like Sea Foam Motor Treatment or STA-BIL to stabilize the gas. This product must be added to gas when it is still fresh. It cannot reverse old fuel. Read more about fuel stabilizers here.

Read more about ethanol and the right gas to use in a push mower where I discuss gas for both push mowers with 2-cycle and 4-cycle engines.

Fuel Restrictions

As mentioned prior, using old fuel can result in clogging issues that will restrict the amount of fuel flowing through the mower. These restrictions are not only caused by running old gas but it is also caused by dirt or debris that gets into the fuel system.

When you are looking for clogged fuel components, check for a plugged fuel filter, clogged fuel line, and fuel pump. If you are getting sufficient fuel flow through these items, move on to the next section and check the carburetor.

For detailed information on checking for fuel restrictions, check out This is Why a Lawn Mower Carburetor Isn’t Getting Fuel.

Dirty Carburetor

The carburetor is used on a push mower to release an amount of fuel to be mixed with air to form combustion in the cylinder. When the carburetor stops functioning properly, the push mower will stop running.

Eventually, a carburetor will wear and just stop working. However, running old gas through it will cause it to stop working prematurely. This is because the varnish and deposits in old fuel cause the small internal components to stick or it causes the fuel jet to become clogged.

To better determine if you are experiencing a running problem due to a dirty carburetor, perform these quick steps:

• Confirm you are getting fuel to the carburetor. Do this by ensuring you are getting sufficient fuel flow to the carburetor. If you are not, check the fuel filter and fuel lines.
• Next, remove the air filter from the air filter housing being careful not to allow any dirt to fall into the air intake.
• Spray carburetor cleaner into the air intake and allow your lawn mower to run. (Don’t use starter fluid). If it runs strong but then begins to run sluggish and possibly shut off, chances are your carburetor is dirty.
• Proceed with disassembling the carburetor and cleaning it.

If you continue to have problems with the carburetor after cleaning it, you may have to rebuild it or replace it with a new carburetor.

Plugged Air Filter

The air filter must always be used on your push mower. It’s a kind of insurance to keep the engine from wearing prematurely. It protects the engine by keeping dirt from entering the air intake.

Because of its importance in protecting the engine, it must be checked and cleaned regularly. If it isn’t, the filter can become so plugged, it keeps sufficient air from getting to the engine. This can cause overheating and the push mower won’t keep running.

I recommend replacing the air filter annually and cleaning it several times throughout the mowing season. When mowing in very dusty conditions, the air filter must be cleaned and replaced more frequently.

Replace the air filter annually and clean it several times throughout the mowing season using these steps for your type of air filter:

Clean a Push Mower Paper Air Filter

• Tap your paper air filter against a solid surface to knock as much dirt out of the air filter as you can remove.
• Hold your paper filter up to a light source and look to see if you can see light shine through the element.
• Reuse a filter when you can see light.
• Replace the filter with a new one when you can’t see any light, the filter is extremely dirty or it is covered in oil.
• Install and reattach the air filter cover.

Clean a Push Mower Foam Filter
(Instructions for a primary filter, not for a pre-filter used in conjunction with a paper filter)

• Wash your foam filter with water and mild dish soap to remove dirt and oil.
• Rinse with water until the soap is removed.
• Lay flat and allow to dry. Placing the filter outdoors in the sun will speed up the drying process.
• Once dry, lightly coat with filter oil.
• If you find your foam filter is brittle, has brown spots, or has been torn, it’s time to replace it with a new filter.
• Install and reattach the air filter cover.

Choke Set in the Wrong Position

The choke is used to restrict airflow when starting a cold engine. This allows a higher concentration of gas-to-air needed for a cold engine than for a warm engine.

Once the engine is started and warms, the choke must be adjusted to the open/run position to allow more air into the cylinder so the engine continues to run. If it isn’t adjusted properly, the push mower will stop running.

Some push mowers have an automatic choke so there isn’t a need to adjust the choke lever to start it. Just because there isn’t a choke lever doesn’t mean there isn’t a problem with the choke.

The choke and linkages can become stuck whether or not you have an automatic or manual choke. In this case, lubricate the choke shaft and linkage with carburetor cleaner so it begins functioning correctly.

Dirty Spark Plug

A fouled spark plug can prevent a push mower from running. When it becomes dirty and coated with carbon, dirt, and oil, the plug will fail to spark. Remove the spark plug and check its condition.

If it is very dark in color or has broken porcelain or burnt electrode, the spark plug must be replaced with a new one.

If the tip is lightly dirty and in good condition, you can proceed with using it, but you need to clean it with a wire brush to remove any carbon and dirt buildup.

Check the gap of the spark plug to make sure it is gapped to the manufacturer’s specification. You can find this information in your owner’s manual.

A spark plug that isn’t gapped correctly or one where the spark plug isn’t securely attached can also result in running problems with your push mower.

Once you confirm you are using a good spark plug or replace it with a new one, proceed with checking your ignition coil if you are still experiencing issues.

Bad Ignition Coil

The ignition coil can cause your push mower won’t stay running. The windings on the ignition coil can separate and short out when the lawn mower gets hot.

This will result in the spark plug not being able to create spark because it is unable to get the voltage it needs. Check for a break in the continuity using an ohmmeter.

Bad Gas Cap

The gas cap on your push mower includes a vent to allow air to pass through the cap. This allows the air pressure to be equalized so the fuel tank doesn’t form a vacuum.

This vacuum will prevent gas from flowing out of the tank through the fuel lines. This will cause the mower to shut down because of a lack of gas in the engine.

Once the mower has stopped running, remove the fuel cap and start your mower. If it starts and runs fine, you may have a problem with the fuel cap vent.

For added confirmation, place the cap back on your fuel tank while allowing your mower to continue to run to see if the mower shuts off after running for a while.

Replace the push mower gas cap with a new one.

Engine Overheats

When a push mower engine overheats, it will shut down and stop running. This could be due to a low engine oil level, the wrong type of oil, a clogged mower deck, or a plugged air filter.

For additional reasons, check out my guide Things That Can Cause a Lawn Mower to Overheat.