Lawn Mower Slows Down When Cutting (3 Major Reasons With Easy Fixes)

A common obstacle faced by many is when the lawn mower slows down when cutting, turning an otherwise straightforward task into a laborious chore.

This article sheds light on the underlying causes and offers practical solutions to rejuvenate your lawn maintenance routine, ensuring your mower’s efficiency and your lawn’s beauty are restored.

Lawn mower slows down when cutting: What to do?

Lawn Mower Slows Down When Cutting: 3 Possible Causes

The struggle with a lawn mower that slows down when cutting is a common, yet solvable problem. As with any machine, understanding the reasons behind its performance issues is critical to resolving them.

While the factors contributing to a lawn mower’s slowdown can be varied, they often boil down to three main categories: blade conditions, engine-related problems, and mechanical issues.

By digging into these areas, you’re well on restoring your lawn mower to its former glory. Let’s delve into each of these potential causes in more detail.

Dull or damaged blades

One of the most common culprits behind a slowing lawn mower is the condition of its blades. Sharp, intact blades are essential for a mower to cut grass swiftly and effectively.

Over time, however, the blades can become dull due to regular wear and tear or from accidentally hitting hard objects such as rocks, branches, or garden debris.

Dull blades demand more power from the mower to cut the same amount of grass, slowing down the machine’s overall speed.

Dull or damaged blades

In addition, blades can get damaged, resulting in bends or nicks that disrupt the smooth operation of the mower. A damaged blade can cause imbalance and excessive vibration during operation, leading to an uneven cut and putting extra strain on the mower’s motor. This undue stress on the motor consequently results in the mower slowing down.

Regularly checking the condition of your mower’s blades and keeping them sharp and undamaged is the first line of defense against a slowdown. Addressing this aspect helps maintain the speed of your mower and ensures a clean, precise cut for your lawn.

Engine-related issues

Aside from blade conditions, a host of engine-related issues could contribute to your lawn mower’s loss of speed. The engine is the heart of your mower, and its smooth functioning is integral to the machine’s performance.

Problems related to low engine power, overheating, a dirty air filter, or clogged fuel lines can significantly reduce the mower’s speed.

Understanding these problems will help you diagnose the issue and apply the right solution. Let’s look at each of these potential issues in more detail.

Engine-related issues

Low engine power

Low engine power can significantly hamper your lawn mower’s performance. The engine might not run at full capacity due to issues like an old spark plug, poor fuel, or a damaged carburetor.

These problems can restrict the engine from generating the power required to rotate the blades effectively, resulting in a noticeable slowdown in cutting speed.

Overheating engine

An overheating engine is another common cause of lawn mower slowdown. Overheating can be caused by low oil levels, a dirty engine, or even operating the mower in extremely hot conditions. When the engine overheats, it cannot function efficiently, decreasing overall performance and speed.

Dirty air filter

The air filter’s role in a lawn mower engine is to prevent dirt, dust, and other debris from entering the engine. Over time, the filter can become clogged with this debris, restricting the airflow to the engine. A dirty air filter means the engine has to work harder to draw in air, which can lead to a decrease in power and consequently a slowdown in operation.

Clogged fuel lines

Just as clean air is vital to an engine’s performance, so is clean fuel. The fuel lines transport fuel from the tank to the engine, but they can become clogged with debris or sediment over time.

This clogging can restrict fuel flow, leading to a lean running condition where the engine doesn’t get enough fuel. This, in turn, leads to reduced engine power and a slowdown in the mower’s speed.

Mechanical problems

While blades and engine issues are often at the forefront of lawn mower problems, we cannot overlook the role that other mechanical components play in the overall performance of your mower.

Worn drive belts, bad spark plugs, loose or damaged pulleys, or a stuck or damaged deck height adjustment mechanism can all contribute to your lawn mower slowing down when cutting.

Delving into these components can further clarify what’s causing your mower’s lackluster performance.

Mechanical problems

Worn drive belt

The drive belt on a lawn mower is responsible for transmitting power from the engine to the wheels or blades. Over time, this belt can wear out or become stretched, resulting in reduced power transfer. A worn drive belt can cause the blades to rotate slower, leading to decreased cutting performance and overall slowing down the mower.

Bad Spark Plugs

Spark plugs play a crucial role in a mower’s engine by igniting the fuel-air mixture to start the combustion process. If a spark plug is faulty or worn out, it can cause poor or intermittent spark, leading to inefficient combustion. This inefficiency can manifest as a lack of power, slowing down the mower significantly.

Loose or damaged pulleys

Pulleys in a lawn mower help transmit the motor’s mechanical power to the blades. If these pulleys are loose or damaged, they can’t effectively transfer power, leading to slow blade rotation. Regularly checking pulleys for any damage or signs of looseness can help maintain the mower’s optimal speed.

Stuck or damaged deck height adjustment mechanism

Finally, the deck height adjustment mechanism plays a crucial role in the effectiveness of the cut. If this mechanism is stuck or damaged, it can cause the mower to operate at an incorrect cutting height, leading to inefficient cutting and increased resistance, which could slow down the mower.

Troubleshooting Steps

While identifying the potential causes behind your lawn mower slowing down is crucial, it’s just the first half of the solution. The next step is rolling your sleeves and applying hands-on remedies to these issues.

Through these troubleshooting steps, you can pinpoint the exact problem, address it directly, and restore your lawn mower’s performance. Let’s embark on restoring your trusty companion to its prime.

Precautions before troubleshooting

Before we dive into the nitty-gritty of troubleshooting your slowing lawn mower, it’s paramount to prioritize safety. Dealing with machinery, even as commonplace as a lawn mower, can carry certain risks if not approached with caution. Here are some essential safety measures to keep in mind:

  • Firstly, always ensure that the lawn mower’s engine is turned off before you start any troubleshooting or maintenance work. An active engine can accidentally start, leading to potential injury.
  • Secondly, disconnect the spark plug wire. This measure provides an additional layer of safety by preventing the mower’s engine from accidentally starting while you’re working on it. It’s a small step that can make a significant difference in ensuring your safety.
  • Finally, during troubleshooting, ensure your lawn mower is positioned on a flat and stable surface. This stability prevents any unnecessary movement of the mower, making it safer and easier for you to work on it. By taking these precautions, you’re creating a safer environment to effectively resolve the issues with your mower.

Step-by-step troubleshooting process

Now that we’ve set the safety measures, it’s time to dive into the hands-on part of our lawn mower revival mission. A step-by-step process helps systematically address potential problem areas, ensuring no stone is left unturned. From inspecting blades to examining the engine and clearing out fuel lines, we’ll tackle these tasks individually.

Step-by-step troubleshooting process

Checking and sharpening blades

Our first stop in this troubleshooting journey is the mower blades. Start by inspecting the blades for any signs of dullness, damage, or debris stuck to them.

If they seem dull or nicked, they likely need sharpening or replacement. Carefully sharpen the edges using a file or a blade grinder, maintaining the blade’s balance. If the damage seems beyond repair, consider replacing the blades.

Inspecting the engine

Next, turn your attention to the engine. Check for visible signs of wear, damage, or dirt accumulation. Pay close attention to the oil level and the condition of the spark plug.

A low oil level can lead to overheating, while a damaged spark plug can cause power issues. Fill up the oil if needed and replace the spark plug if it appears worn out or faulty.

Checking Engine Power

To check engine power, start the mower and listen to its sound. A properly running engine should have a smooth, consistent sound. If it sputters or sounds weak, it might run lean (not getting enough fuel), indicating a potential issue with the fuel system or the spark plug.

Cleaning or Replacing the Air Filter

A clean air filter ensures efficient airflow to the engine, boosting its performance. Remove the air filter and inspect it. If it’s mildly dirty, clean it with a soft brush or wash it with mild soap and water. However, if the filter appears very clogged or damaged, replace it with a new one.

Clearing Clogged Fuel Lines

Finally, inspect the fuel lines. If your mower has a transparent fuel line, look for visible clogs. If not, you may need to detach and manually inspect the line for blockages. Use a long, flexible brush to clean the line or consider replacing it if it appears damaged or extremely clogged.

Inspecting mechanical components

Having inspected the blades and the engine, let’s focus on other mechanical components. The overall performance of your lawn mower isn’t just determined by how well its engine runs or how sharp its blades are, but also by the efficiency of the various mechanical parts that work together to ensure a smooth operation.

Inspecting mechanical components

Inspecting and Replacing the Drive Belt

Begin by examining the drive belt, the critical part responsible for transmitting power from the engine to the blades or wheels. Look for any signs of wear, tear, or stretching.

If the belt appears damaged or overly worn, replace it with a new one. Even if it looks okay but your mower’s been losing power, it may be worth replacing the belt anyway – an old belt can often be the hidden culprit behind decreased mower performance.

Tightening or Replacing Pulleys

Next, check the pulleys. These components transfer the motor’s mechanical power to the blades. If these are loose, they cannot effectively transfer power, leading to slow blade rotation and an overall slowdown of the mower.

Tighten any loose pulleys, and replace them if they appear damaged or overly worn.

Inspecting and Lubricating the Deck Height Adjustment Mechanism

Finally, check the deck height adjustment mechanism. This mechanism is essential for ensuring the mower cuts at the correct height.

If it’s stuck or damaged, it can cause the mower to operate inefficiently. Lubricate the mechanism to ensure smooth operation and, if necessary, consult your lawn mower’s manual or a professional for further assistance.

Pro Tips for Preventing Lawn Mower Slowdown

Once you’ve tackled the issues causing your lawn mower’s slowdown, you’d ideally like to keep it operating smoothly. Prevention, as they say, is better than cure.

Here are a few expert tips to ensure your lawn mower stays at the top of its game and you can prevent the slowdown from recurring.

Pro Tips for Preventing Lawn Mower Slowdown

Regular maintenance and servicing

The key to a well-functioning lawn mower is regular maintenance. This involves timely oil changes, blade sharpening, air filter cleaning or replacement, spark plug checks, and regular inspections of the belts and pulleys.

By staying proactive about these tasks, you can nip any potential problems before they escalate to more significant issues causing the mower to slow down.

Proper usage techniques

Proper usage goes a long way in extending the life and efficiency of your lawn mower. Try not to cut wet grass as it can stick to the blades and the deck, affecting the mower’s performance.

Also, don’t rush the mowing process. Let the mower cut at its own pace to prevent overwhelming the engine and the blades.

Maintaining a clean and debris-free cutting deck

Ensure the cutting deck is clean and free of debris after every use. Clippings left on the deck can harden over time, making it harder for the blades to rotate and affecting the mower’s cutting performance. A quick clean-up after each mow can save you from future slowdown issues.

Frequently Asked Questions (fAQs)

Why is my lawn mower losing power when cutting thick grass?

Your mower may struggle with thick grass due to dull blades, low engine power, or clogged deck. Sharpen blades, perform engine maintenance, and clean your deck regularly for optimal performance.

Can a bent blade cause a lawn mower to slow down?

Yes, a bent blade can disrupt the mower’s balance, leading to engine stress and eventual slowdown. It can also affect the cut quality, causing uneven or missed patches in your lawn.

How often should I sharpen my lawn mower blades?

It’s generally recommended to sharpen mower blades once or twice per mowing season, or whenever you notice a decline in the quality of the cut, such as ragged, uneven grass tips.

How can I prevent grass clippings from clogging the mower deck?

Prevent clippings from clogging your mower deck by avoiding mowing wet grass, regularly cleaning the deck, and using a blade that mulches clippings into smaller pieces, reducing the chance of clogs.

Should I attempt repairs myself or consult a professional?

Minor repairs like sharpening blades or replacing filters can be done at home. However, it’s best to consult a professional for more complex issues like engine trouble or mechanical component replacement.


In conclusion, a slowing lawn mower can be attributed to several causes, such as dull blades, engine issues, or mechanical problems.

You can enhance your mower’s performance by understanding the root of the problem and taking necessary troubleshooting steps.

Regular maintenance, proper usage, and keeping the deck clean are crucial for preventing such issues. Always seek professional help for complex issues to ensure your mower’s longevity.

We hope that this guide has been helpful. You can read about similar topics here on our website. Check back again soon for more.

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