12 Reasons Your Push Mower Loses Power: SOLVED!

You really get to know your push mower when you’re using it once or twice a week through the most demanding part of the mowing season.

You know it so well, you can tell when the engine isn’t running just right and your mower isn’t giving you the power it used to. Not only will an underperforming push mower run sluggishly, it will also give you a bad cut.

A push mower will lose power when air or fuel is not getting to the engine or the mower is being overworked. This can be the result of old fuel; a plugged fuel or air filter; a clogged fuel line; a dirty carburetor; a low engine oil level; plugged mower deck; slow engine speed; or fast ground speed.

Refer to your owner’s manual for all safety precautions that must be taken when working on your model push mower to avoid injury.

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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.

12 Reasons Your Push Mower Loses Power

Clogged Air Filter

When the engine can’t get sufficient clean air, your push mower will sputter and possibly die. The air filter is the first thing I check when a push mower is experiencing a loss of power.

An air filter can become plugged restricting the amount of air that gets to the engine. The air filter is required to protect your engine by keeping dirt and debris from entering the air intake.

The air filter should be replaced annually when completing a full service on your push mower. But you’re not done there. You must clean it a couple of times through the mowing season so it continues to work.

You may have to clean or replace your air filter more frequently if you are mowing in dusty conditions or you mow more than the average push mower owner. Never operate your mower without an air filter even if it is only for a short period while you wait for a new filter.

Dirt in your engine can cause scoring of the cylinder and piston ring damage resulting in a significant repair bill that may be more than the cost of a new mower.

Clean a paper push mower air filter:

• Remove the air filter from the air filter housing.
• Wipe out any remaining dirt in the housing with a dry cloth. Be careful not to allow dirt to fall into the air intake.
• Tap your air filter against a solid surface to knock as much dirt loose as possible.
• Hold your filter up to a light source.
• Reuse your filter if you can see light through the paper element.
• Replace with a new filter if you can’t see light through the paper element.
• Reattach the air filter housing cover.

Clean a foam push mower air filter:

• Remove the filter for the air filter housing.
• Wipe out any dirt that is still in the housing. Don’t let any dirt fall into the air intake.
• Inspect your filter for usability. If it is dry, brittle, has a dark spot, or is torn, purchase a new filter for your push mower.
• If your filter is in good shape, wash it with mild dish soap and water to remove dirt and oil on the filter. Rinse until the water runs clear.
• Let the filter air dry. Laying it out in the sun will speed up the drying process.
• Once dry or if you are using a new filter, lightly saturate your filter with a foam filter oil. The whole filter needs to be covered with oil, but you don’t want it to be dripping with oil. Use a paper towel to absorb excess oil if needed.
• Place the filter in the air filter housing and reattach the cover.

Bad or Old Fuel

Old gasoline can cause a fuel restriction in your mower resulting in a push mower losing power. Gas can begin to break down and become less effective as soon as 30 days after purchase.

Because of this, it is important to consume the gas you purchase timely or add a fuel stabilizer to your fuel if it will not be consumed within 30 days.

Most gasoline sold today contains ethanol. This is an environmentally friendly fuel. While it is okay to use in most vehicles, it can be harmful to the small engine used on a push mower.

Ethanol naturally attracts moisture from the air that can cause gumming in the fuel system alone.

Here are a few tips to take when purchasing gas for your push mower:

• Buy fuel from a busy gas station.
• Use unleaded gasoline with a minimum octane rating of 87 and maximum ethanol content of 10 percent. The lower the ethanol content, the better.
• Add a fuel additive to stabilize your gasoline and reduce moisture.
• Store any remaining fuel in a cool dry area away from the outdoor elements.

Remove old fuel from your push mower using a fuel siphon. Fill with fresh gasoline for 4-cycle engines. If you have an older push mower that runs a 2-cycle engine, make sure you are using the correct ratio of oil to fuel in your mower.

To learn more about gasoline and fuel additives read these articles: “Why Use Sea Foam Additive in a Lawn Mower” and “This is the Gas Your Push Mower Uses”.

Bad Spark Plug

A fouled spark plug can cause an intermittent spark that can cause a loss of power. Inspect your spark plug for signs of carbon, dirt, and oil buildup on the tip.

If you find a dirty or damaged spark plug, I recommend replacing it with a new one to ensure you’re running a good plug in the mower.

Alternatively, if it’s only dirty and not very dark in color, you can attempt to clean it with a wire brush and reuse it.

Clogged Fuel Filter or Fuel Lines

Not all push mowers use a fuel filter to keep dirt from entering the fuel system. If your mower does, check it to make fuel is able to flow through the filter and it isn’t plugged.

Replace the fuel filter if you find it plugged. The new filter must be installed with the arrow on the side of the filter pointed in the direction of the fuel flow.

Check for a blockage in the fuel lines. Do this by starting and stopping fuel flow while you check each section of the fuel line.

Check for fuel line blockage:

• Stop your fuel flow using pinch pliers or the fuel shut-off valve (if your push mower uses one).
• Identify a section of the fuel line you want to check.
• Remove the end of the line that is furthest from the fuel tank.
• Place the end in a container. This container must be placed lower than the fuel tank. This is because fuel will flow using gravity. It cannot run uphill without the use of a fuel pump.
• Start your fuel flow allowing fuel to run into the container.
• If you are getting good fuel flow, stop the flow and reattach your fuel line.
• If you are not getting good fuel flow, stop the flow and follow the directions to clear the blockage.

Remove a fuel line restriction:

• With the fuel flow turned off, remove the section of the fuel line from your mower.
• Spray carburetor cleaner into the line to loosen the clog.
• Follow this by blowing compressed air into the line to remove the clog.
• Repeat using carburetor cleaner and compressed air until the line no longer is clogged.
• If you are unable to remove the restriction, install a new fuel line.

Dirty Carburetor

A carburetor’s purpose is to regulate the fuel and air mix required to form combustion in the engine.

When the carburetor becomes dirty from running old fuel through your push mower, components in your carburetor can become clogged preventing a sufficient supply of fuel from getting to the engine.

Disassemble the carburetor and clean it to remove fuel restrictions caused by gumming and hard crusty deposits. Check your components to make sure they are in good working condition.

If you are a little mechanical, follow my instructions in this guide to clean a push mower carburetor. You may also choose to have a small engine repair shop perform this for you.

If the carburetor still fails to correctly supply fuel, you will have to replace the carburetor assembly.

Engine Power is Too Slow

Your push mower deck requires full engine power to run. The throttle must be set to the “fast” position when your mower deck is engaged. Check your throttle lever to make sure it is in the correct position.

Low Engine Oil

When the engine oil in your push mower is at a low level, there isn’t enough lubrication to keep the moving parts in your engine moving freely.

Increased friction can build heat in the engine causing a power loss. If a low engine oil level isn’t caught quickly enough, it can result in a significant engine repair bill.

Because of the damage a low engine oil level can cause to your push mower, it is good practice to check the engine oil level before each mowing. Doing so may catch engine problems at an early stage before it develops into a larger issue.

To fix this, bring your engine oil level to the correct level using the lines on your dipstick for reference. If you caught your problem soon enough, you may be able to fix it by adding engine oil and identifying the reason why your engine level is low.

If you didn’t catch it early, you could have serious engine damage that should be diagnosed by an experienced small engine mechanic.

Too Much Engine Oil

Overfilling the crankcase with engine oil will cause your engine to smoke. Increased pressure builds as a result of too much engine oil and oil can be pushed into the cylinder through the valve train. When this happens, a bluish-white smoke is emitted when the oil burns in the cylinder.

This thick cloud of smoke can plug your air filter causing running issues because your engine isn’t able to get the clean air it needs. Check your air filter and your spark plug, and clean or replace them if needed.

Continuing to run your push mower with too much oil can cause seal damage, the engine to hydro lock, and a bent piston rod. Correct an engine with too much oil by removing a little oil.

You can do this by using an oil evacuator, a drain plug, or even a turkey baster.

Ground Speed is Too Fast

Mowing your lawn at too fast a speed will cause your mower to have to work harder causing it to lose some power. Your engine works harder to cut thick lawns than it does to cut thinly covered lawns.

Adjust your speed to your mowing conditions to not overwork or overheat your engine.

Cutting Wet or Tall Grass

Avoid cutting wet or tall grass as this will strain the engine causing a poor cut and extra load on the engine. Mowing grass when it is dry will reduce the amount of grass clippings collecting under the deck.

To mow taller grass, adjust the cutting height to its highest height and make your first cut. Follow it by lowering your mower deck and making a second cut.

If your grass is extremely tall, I recommend using a walk-behind brush cutter to cut down the grass and make it manageable going forward.

Check out your local rental center for options to rent a brush cutter. You can read more about cutting tall grass in this article.

Clogged Mower Deck

Keep your mower deck clean and free of grass clippings and debris so your blades can spin freely. The engine will lose power when it is required to work hard to turn blades through a deck packed with debris.

Scrape your mower deck regularly to remove debris collecting under the deck. The area under the deck uses the air movement created by the blades to form a suction to stand the grass tall for a good cut.

A clogged mower deck not only causes a loss of power, but it also creates a bad cut because it restricts air movement under the deck.

Dull Mower Blades

A dull mower blade can further magnify the power loss you experience when not only does the engine need to turn blades into a deck packed full of debris, but it now how to turn dull blades through this debris.

Remove your mower blades and sharpen the blades using this guide for your push mower blades. Mower blades need to be sharpened at least after every 25 hours of use. They may need to be sharpened more frequently when using your mower in sandy or gravel conditions.

In Summary

Performing routine maintenance on your push lawn mower and checking your engine oil before you mow can prevent engine problems that cause a loss of power.

If none of the items above solve your power loss problem, take your mower to the local small engine mechanic to be looked at. There are internal engine problems that are hard for the homeowner to diagnose without the proper engine tools to accurately perform tests on the engine.