Is Your Lawn Mower Surging? Here’s How to Fix It!

The warm weather is finally here, and you’re ready to get your lawn looking its best. You fire up your trusty lawn mower, but instead of a smooth purr, you’re met with a frustrating surge – the engine revving up and down erratically. It’s enough to make you want to throw your hands up in frustration. But don’t despair! This article will guide you through the common causes of lawn mower surging and equip you with the knowledge to diagnose and fix the problem, saving you time, money, and frustration. We’ll cover everything from identifying the problem to troubleshooting and replacing parts, so you can get your lawn mowed in no time.

What is Lawn Mower Surging?

Lawn mower surging occurs when the engine speed fluctuates uncontrollably. The engine might rev up to high speeds and then suddenly drop down, creating an uneven and frustrating mowing experience. It can be caused by various factors, including problems with the fuel system, ignition system, or even a clogged air filter.

Understanding the Root Causes of Surging

Before jumping into repairs, it’s crucial to understand what’s causing the surging. The most common culprits are:

1. Fuel System Issues

  • Clogged Fuel Filter: A dirty or clogged fuel filter restricts fuel flow to the engine, leading to inconsistent fuel delivery and surging.
  • Dirty Carburetor: The carburetor mixes fuel and air, and over time, it can get clogged with dirt and debris. This causes a lean fuel mixture, leading to surging.
  • Bad Fuel: Old, stale gasoline can gum up the fuel system and cause surging. Ethanol in gasoline attracts moisture, which can form a gummy residue in the carburetor and fuel lines.

2. Ignition System Problems

  • Faulty Spark Plugs: A worn-out or fouled spark plug can prevent a clean spark, disrupting the combustion process and causing surging.
  • Loose or Damaged Spark Plug Wires: Worn or damaged spark plug wires can impede the flow of electricity to the spark plugs, causing weak or inconsistent sparks.
  • Faulty Ignition Coil: The ignition coil generates high voltage to power the spark plugs. A failing ignition coil can produce weak sparks, leading to erratic engine performance and surging.

3. Air Intake System Issues

  • Clogged Air Filter: A dirty air filter restricts airflow into the engine, causing a lean air-fuel mixture and surging.

4. Other Potential Causes

  • Fuel Line Restrictions: Kinks or blockages in the fuel lines can restrict fuel flow and lead to surging.
  • Incorrect Fuel-Air Mixture: A carburetor adjustment problem can result in a fuel-air mixture that is too rich or too lean, leading to surging.
  • Engine Problems: In some cases, internal engine problems, such as worn piston rings or a damaged valve, can also contribute to surging.

Troubleshooting and Fixing the Surging Problem

Now that you understand the possible causes, let’s dive into troubleshooting your surging lawn mower.

1. Inspect the Fuel System

  • Check the Fuel Filter: Remove the fuel filter and inspect it for dirt or debris. If it’s dirty, replace it with a new one.
  • Clean the Carburetor: If the fuel filter is clean, the problem might lie with the carburetor. Depending on your carburetor type, you may need to use a carburetor cleaner or disassemble the carburetor to clean it thoroughly. You can find plenty of online tutorials on how to clean specific carburetor models.
  • Replace Old Fuel: If your fuel is more than 30 days old, it’s time to drain it and refill with fresh, high-quality gasoline.

2. Inspect the Ignition System

  • Inspect the Spark Plugs: Remove the spark plugs and inspect them for wear, fouling, or damage. If they are worn, fouled, or damaged, replace them with new ones that match your engine specifications.
  • Check the Spark Plug Wires: Carefully inspect the spark plug wires for cracks, fraying, or loose connections. Replace any damaged or worn wires.
  • Test the Ignition Coil: You can test the ignition coil with a multimeter to confirm if it’s functioning properly. If it’s faulty, it will need to be replaced.

3. Inspect the Air Intake System

  • Clean the Air Filter: Remove the air filter and inspect it for dirt and debris. Clean or replace it as needed.

4. Additional Checks

  • Inspect Fuel Lines: Check the fuel lines for kinks, blockages, or leaks. If you find any issues, repair or replace the lines as needed.
  • Adjust the Carburetor: If you’re comfortable with carburetor adjustments, you might need to adjust the mixture screws to get the proper fuel-air ratio. Consult your owner’s manual or an online guide for specific instructions for your model.

When to Seek Professional Help

While most lawn mower surging issues can be tackled with a little DIY knowledge, some situations require professional assistance. If you’ve tried the troubleshooting steps above and still can’t identify the cause or fix the problem, it’s time to contact a qualified lawn mower repair technician. Here are some signs that you might need professional help:

  • Internal engine damage: If you suspect an internal engine issue, such as worn piston rings or a damaged valve, it’s best to leave repairs to a professional.
  • Complex carburetor issues: If your carburetor is very dirty or needs a major rebuild, it’s best to take it to a mechanic.
  • Specialized tools: Some repairs might require specialized tools or knowledge, which are better left to a professional.

Preventing Surging in the Future

Once you’ve fixed the surging problem, it’s important to take steps to prevent it from happening again. Here are some tips:

  • Use high-quality gasoline: Always use fresh, high-quality gasoline.
  • Maintain a regular cleaning schedule: Clean the air filter, spark plugs, and carburetor regularly.
  • Store your lawn mower properly: Drain the fuel tank and carburetor before storing your lawn mower for the off-season.
  • Read your owner’s manual: Familiarize yourself with the recommended maintenance schedule for your specific lawn mower model.


Surging lawn mowers can be a frustrating problem, but with a bit of patience and the right knowledge, you can often fix the issue yourself. By understanding the common causes and following the troubleshooting steps outlined in this guide, you can diagnose and repair the problem and get your lawn mower running smoothly again. Remember, if you encounter complex issues or aren’t comfortable with DIY repairs, don’t hesitate to seek professional help.


What causes a lawnmower to surge?

A surging lawnmower is often a symptom of a fuel-related issue. The most common cause is a clogged carburetor, which prevents the engine from receiving the correct amount of fuel. This can be due to dirt, debris, or old fuel. Another possibility is a problem with the fuel filter, which can become blocked and restrict fuel flow. Finally, a faulty fuel pump can also lead to surging, as it may not be delivering enough fuel to the carburetor.

If your lawnmower is surging, it’s important to diagnose the problem as soon as possible to prevent further damage. Ignoring the issue can lead to engine damage or even a complete engine failure.

How do I clean a lawnmower carburetor?

Cleaning a lawnmower carburetor is a relatively simple process that can be done by most homeowners. First, you’ll need to remove the carburetor from the engine. This typically involves removing a few screws and disconnecting the fuel lines. Once the carburetor is removed, you can clean it using a carburetor cleaning kit or a spray cleaner. Be sure to follow the instructions on the cleaner carefully.

After cleaning the carburetor, you’ll need to reassemble it and reinstall it on the engine. Make sure all connections are tight and that the fuel lines are securely attached. Once the carburetor is installed, you can start the engine and test it.

What happens if the fuel filter is clogged?

A clogged fuel filter can cause a variety of problems with your lawnmower, including surging. When the filter is clogged, it restricts fuel flow to the carburetor, which can cause the engine to run poorly. In severe cases, a clogged fuel filter can even cause the engine to stall.

If you suspect that your fuel filter is clogged, you should replace it as soon as possible. This is a relatively inexpensive repair that can save you a lot of trouble down the road.

How do I know if the fuel pump is faulty?

A faulty fuel pump can be difficult to diagnose, but there are a few signs that might indicate a problem. One common symptom is surging, as the fuel pump may not be delivering enough fuel to the carburetor. Another sign is a decrease in engine power, as the engine may not be getting enough fuel to run properly.

If you suspect that your fuel pump is faulty, you should have it checked by a qualified mechanic. Replacing the fuel pump is a more complex repair, and it’s best to leave it to a professional.

How can I prevent my lawnmower from surging in the future?

There are a few things you can do to help prevent your lawnmower from surging in the future. First, be sure to use fresh, clean fuel. Old fuel can gum up the carburetor and cause problems. Second, keep the fuel tank and carburetor clean. Regularly cleaning these components will help prevent clogs and ensure that the engine is getting the fuel it needs.

Finally, have your lawnmower serviced regularly. A qualified mechanic can inspect the fuel system and make sure everything is in good working order. This will help to prevent problems before they occur and keep your lawnmower running smoothly.

What if the surging problem persists even after cleaning the carburetor and fuel filter?

If your lawnmower is still surging after cleaning the carburetor and fuel filter, there could be a more serious problem with the engine. In this case, it’s best to take your lawnmower to a qualified mechanic for diagnosis and repair.

They can inspect the engine for other potential issues, such as a faulty ignition system, a damaged spark plug, or a worn-out piston. Depending on the severity of the problem, they may need to perform more complex repairs.

Is there any way to troubleshoot the surging issue myself?

While troubleshooting a surging lawnmower can be challenging, there are a few things you can try before taking it to a mechanic. Start by inspecting the fuel lines for any leaks or cracks. You should also check the air filter to ensure it’s clean and not restricting airflow.

If you’ve recently added fuel, consider draining the tank and refilling it with fresh, clean fuel. If none of these steps resolve the issue, it’s highly recommended to seek professional assistance from a qualified mechanic. They can diagnose the problem accurately and perform any necessary repairs.

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