It can be tricky to figure out why a lawn mower loses power when cutting the lawn. Most lawn mowers are fairly simple tools, but many owners are not familiar with working on them.

Learning to solve problems with your lawn mower is easy, and this article will help you solve one of the most frustrating problems you are likely to encounter: a mower that loses power.

There are several steps you can take to stop a lawn mower from cutting out when you are mowing.

Why Does Your Lawn Mower Lose Power When Cutting?

A lawn mower that loses power when cutting is typically caused by one or several reasons, and most of the time the solution is simple. In order to troubleshoot the cause of the problem, you’ll need to start by identifying the common causes of small engine power loss. You will need to know the different parts of your lawn mower.

You must exercise care any time you are working on a lawn mower. Do not operate a mower without proper safety guards covering the blades and the mower on a flat surface on its wheels. Serious injuries including burns and death can occur if you fail to work on a mower safely.

Identifying the Cause

The first step to identifying why your lawn mower loses power when cutting the lawn is identifying when the problem happens.

The problem can happen intermittently or constantly, and the causes will be different. Most of the common causes of a mower losing power only apply to gasoline-powered lawn mowers.

– Electric Mower Losing Power

The most common cause of loss of power from an electric lawn mower is accumulated dirt and debris in the mower blade housing. Over time, grass clippings and dust mix in the area that encloses the mower blade. This mixture can become an unbelievably solid mass almost like concrete. It can cause drag on the mower blades and the shaft that attaches the engine to the blade.

A common reason for material to get packed into the housing is the failure to dump the grass collecting bag often enough. When the bag is overfull, there is no place for the grass clippings to go and they get crammed into the housing.

The same problem can arise when cutting wet grass. The moisture causes the grass clippings to bind up and the lawn mower can’t push the wet grass into the bag. It always best to avoid cutting wet grass.

Clearing the blade housing is easy, but be sure to follow basic safety protocols to avoid serious injury.

With the mower unplugged, tilt it on its side. Wear gloves to prevent cutting yourself on the mower blade. Use a scraper or screwdriver to remove the mass, being sure to clean around the propeller shaft. When the housing is clear, set the mower upright and plug it in. Test it to see if it is now working correctly.

Another common failure that will cause an electric lawn mower to cut out is damage to the cord the mower is connected to. Check for slits, cuts, and cracks in the extension cord, and also make sure there is no evidence of melting at the plug. These are all potential causes of damage that causes loss of power. You should replace or repair a damaged power cord whenever you suspect a problem.

– Gasoline Lawn Mower Losing Power

Gasoline mowers present more opportunities for problems that can cause the mower to not run at full power. Just like with electric mowers, you should also check a gasoline lawn mower blade housing for built-up dirt. Just be sure to drain the gas tank first to prevent spillage of fuel and a potential fire.

Common Causes of Power Loss

Small gasoline engines used in lawn mowers are simple designs, but they do have a few critical flaws. It’s essential to understand how gasoline engines function to find the problems easily. We will explain the basic function of your lawn mower engine to help you when it loses power while cutting.

All gasoline engines require three components to run. Those components are fuel, air, and ignition. All of the common reasons a lawn mower loses power can be attributed to problems within these three areas.

In the most basic terms, air is drawn through the air filter where it mixes with fuel in the carburetor before it’s sucked into the combustion chamber. The piston compresses the air and fuel mixture which is then ignited by the spark plug. Energy is created by the turning of the engine to turn the mower blade.

– Air Restrictions

The first thing you should check if your mower is losing power is the air filter. The filter is usually held in place by two or three screws. Your lawn mower manufacturer should specify the frequency of which you should change the filter. To clean an air filter, use compressed air to blow dirt from the opposite side as the air flows.

With the air filter removed, you will be able to see the carburetor. If the inner surface is clumped with dirt, you should clean the carburetor. Typically, the carburetor can be removed by a couple of bolts and removal of the fuel line. You can buy a carburetor cleaner at your local auto parts store. Clean the carburetor according to the directions.

– Fuel Restrictions

Dirt can accumulate in the fuel tank due to poor quality fuel from dirty gas cans and from use in dirty areas. Dirt will cause a wide range of problems, including loss of power. Dirt in the carburetor causes sputtering and sudden loss of power. The motor may die, then restart and run fine for a while before cutting out again. Surging idle is a common symptom of dirt in the fuel system.

Cleaning the fuel system is easy. You will need to remove the fuel tank from the mower to clean it. You can use a carburetor cleaner to rinse the fuel tank free of debris. It’s usually easier to replace the fuel line than cleaning it. If you have dirt in the fuel tank, you will also need to clean the carburetor making a special effort to ensure the orifice where fuel enters the mouth of the carb is clean.

– Spark Problems

In order for the air and fuel to be ignited, the spark plug must be in good working condition and adjusted correctly. Over time, a spark plug will wear out. Eventually, the spark will no longer be powerful enough to fully ignite the air and fuel. You are likely to notice power loss including bogging down when cutting grass because of a worn spark plug.

Removing and replacing a spark plug is easy. Remove the plug wire by gently pulling on the boot, not the wire. Use a spark plug socket to remove the plug.

To inspect the spark plug, look at the tip. If you see evidence of burns, chips, or any other damage, discard and replace the plug. If the plug is black, it could indicate a dirty air filter or an oil leak inside the engine. Bright white plugs indicate the engine isn’t getting enough fuel. This can happen because of obstructions in the carburetor or fuel line.

– Less Common

Rarely, the muffler can become obstructed and cause a serious loss of power. This is most common after storing a lawn mower for a period of time. Animals sometimes make nests in the muffler, causing obstructions.

A problem that can cause a lot of power loss is the failure to change the oil. Over time, bearings and seals will fail, causing the engine to seize. If the engine is making knocking sounds when it’s running, it probably needs a major overhaul.

Reasons a Lawn Mower Bogs Down in Thick Grass

Any of the above problems can cause your lawn mower to bog down in thick grass. In order for your lawn mower to be effective, it must be in good working order. If you don’t service your mower from time-to-time, your lawn mower will lack power.

Sometimes, there are other issues that can cause your mower to not work well, particularly when cutting thick grass. The lawn mower blade itself can become damaged and worn over time. If the blade doesn’t have major knicks, it can be sharpened. Severely damaged mower blades can be replaced. You should follow careful safety practices when replacing a mower blade.

When mowing tall grass, you want to increase the engine speed for more power. A stuck or sticky throttle cable can prevent the engine speed from being increased, which can cause the motor to bog down in thick lawn or when mowing dense weeds.


There are a number of causes for a lawn mower to lose power when cutting that you can easily solve yourself. The guide above shows you how easy it is to diagnose the cause of the problem.

The best thing you can do is to properly service your lawn mower at least once a year. An oil change is easy to do yourself.

The cost of an air filter and a spark plug, along with the few minutes it takes to ensure the carburetor is clean will keep the lawn mower in excellent running condition for many years.

If your lawn mower starts to lose power and bog down when cutting the grass, you should find the problem and correct it. Neglecting a lawn mower that is bogging down will eventually lead to bigger problems and the need to replace the lawn mower.

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