Why Does My Lawn Mower Keep Surging?

There’s nothing quite as frustrating as trying to mow your lawn and having your trusty mower sputter and surge, leaving you with an uneven cut and a sense of defeat. Why does this happen? What’s the culprit behind this annoying lawn mower behavior? This article will delve into the common reasons why your lawn mower keeps surging, providing you with troubleshooting tips and potential solutions to get your mower back in tip-top shape. We’ll explore everything from fuel issues to engine problems, offering practical advice to help you diagnose and fix the problem.

A quick overview: Your lawn mower is surging because there is an issue with the fuel-air mixture going to the engine. This can be caused by a variety of issues, including a clogged air filter, a dirty carburetor, a bad spark plug, or even a fuel line problem. By understanding the possible causes and using the troubleshooting tips provided, you can pinpoint the problem and get your mower back to smoothly cutting your grass in no time.

Fuel Issues: The Root of the Problem

Fuel is the lifeblood of your lawn mower, and any issues with its supply or quality can lead to surging. Here’s a breakdown of the most common fuel-related culprits:

1. Old or Contaminated Fuel

Old fuel, especially gasoline, can become stale and gum up your mower’s carburetor, leading to inconsistent fuel delivery and surging.


  • Use fresh fuel: Always use fresh, high-quality gasoline.
  • Store fuel properly: If you’re storing fuel for extended periods, consider using a fuel stabilizer to prevent deterioration.
  • Drain old fuel: If you suspect your fuel is old, drain it and replace it with fresh fuel.

2. Clogged Fuel Filter

The fuel filter traps debris and sediment, preventing it from reaching the carburetor. A clogged fuel filter can restrict fuel flow, leading to a lean fuel mixture and surging.


  • Inspect the filter: Check the fuel filter regularly for signs of clogging.
  • Replace as needed: Replace the filter if it’s dirty or damaged.

3. Dirty Carburetor

The carburetor mixes fuel and air, and a dirty carburetor can disrupt this process, leading to surging.


  • Clean the carburetor: This can involve disassembling the carburetor, cleaning the components, and reassembling it.
  • Consider a rebuild kit: If the carburetor is severely clogged, you may need to replace it or rebuild it with a carburetor rebuild kit.

Engine Problems: The Engine’s Not Running Smoothly

While fuel problems are common, engine issues can also contribute to surging. Here are a few engine-related problems to investigate:

1. Air Filter Issues

A clogged air filter restricts airflow, which can cause a lean air-fuel mixture and lead to surging.


  • Inspect the filter: Check your air filter regularly and replace it if it’s dirty or damaged.

2. Spark Plug Problems

A fouled or worn-out spark plug can misfire, leading to inconsistent engine performance and surging.


  • Inspect the spark plug: Remove the spark plug, inspect it for signs of fouling or wear, and replace it if necessary.
  • Adjust the gap: Ensure the spark plug gap is set correctly for your mower’s engine.

3. Ignition Issues

Problems with the ignition system, such as a faulty ignition coil or a malfunctioning ignition switch, can disrupt the spark delivery and cause surging.


  • Check the spark plug wires: Ensure they’re properly connected and show no signs of wear or damage.
  • Inspect the ignition coil: Look for any cracks or damage. If the ignition coil is faulty, it will need to be replaced.

Troubleshooting Tips: Getting to the Root of the Problem

Here are some general tips to help you troubleshoot your surging lawn mower:

  • Start with the basics: Make sure the fuel tank is full, the engine oil is at the correct level, and the spark plug is properly connected.
  • Listen for unusual noises: Listen carefully for any unusual sounds coming from the engine, such as rattling, knocking, or hissing.
  • Check for fuel leaks: Inspect the fuel lines and connections for leaks.
  • Test the spark plug: Remove the spark plug and ground it to the engine block. Start the engine and check for a strong blue spark.
  • Consider a professional: If you’re unsure about the problem or you’re not comfortable working on your mower, it’s best to take it to a qualified mechanic.

Preventing Surging: Maintenance is Key

Regular maintenance can help prevent your lawn mower from surging. Here are some key steps:

  • Change the air filter: Replace the air filter regularly, depending on the usage of your mower.
  • Clean the carburetor: Clean the carburetor every season or as needed.
  • Check the spark plug: Inspect and replace the spark plug as recommended in your mower’s owner’s manual.
  • Store the mower properly: When storing your mower for an extended period, drain the fuel tank and run the engine for a few minutes to empty the carburetor.

Conclusion: Smooth Sailing on Your Lawn

While a surging lawn mower can be a frustrating experience, it doesn’t have to be a mystery. By understanding the common causes of surging and using the troubleshooting tips provided in this article, you can effectively diagnose and fix the problem. Remember, regular maintenance is key to preventing surging and ensuring your mower runs smoothly for years to come. With a little effort and attention, you can have your lawn looking pristine in no time!

Frequently Asked Questions

Why does my lawnmower keep surging?

Lawn mower surging is a common problem that can be caused by a variety of factors. The most common causes include a clogged air filter, a dirty carburetor, or a faulty fuel line.

To fix a surging lawnmower, you will need to troubleshoot the problem and identify the root cause. Once you have identified the problem, you can then take steps to fix it. For example, if the problem is a clogged air filter, you will need to replace the air filter. If the problem is a dirty carburetor, you will need to clean the carburetor. And if the problem is a faulty fuel line, you will need to replace the fuel line.

What are the signs of a surging lawnmower?

A surging lawnmower will often run erratically, with the engine speed fluctuating up and down. This can make it difficult to mow your lawn, as the mower may suddenly speed up or slow down.

In addition to the engine speed fluctuating, you may also notice that the mower is difficult to start or that it stalls frequently. If you notice any of these signs, it is important to troubleshoot the problem and fix it as soon as possible.

What causes a lawnmower to surge?

There are many reasons why your lawnmower might be surging, but the most common include:

  • Clogged air filter: A dirty air filter can restrict airflow to the engine, causing it to surge.
  • Dirty carburetor: A dirty carburetor can cause the fuel-air mixture to be incorrect, leading to surging.
  • Faulty fuel line: A cracked or kinked fuel line can restrict fuel flow to the engine, causing it to surge.
  • Spark plug issues: A fouled or worn-out spark plug can cause the engine to misfire, leading to surging.
  • Fuel issues: Old or contaminated fuel can also cause surging.

How do I fix a surging lawnmower?

The first step is to identify the cause of the surging. This can be done by checking the air filter, carburetor, fuel lines, and spark plug. Once you have identified the problem, you can take steps to fix it.

For example, if the air filter is dirty, you will need to replace it. If the carburetor is dirty, you will need to clean it. If the fuel line is faulty, you will need to replace it. And if the spark plug is fouled or worn out, you will need to replace it.

What are some preventative measures to prevent surging?

There are a few things you can do to prevent your lawnmower from surging.

  • Change the air filter regularly: The air filter should be changed every 25 hours of use or as needed.
  • Clean the carburetor regularly: The carburetor should be cleaned every 100 hours of use or as needed.
  • Use fresh fuel: Old or contaminated fuel can cause surging, so it is important to use fresh fuel.
  • Maintain your lawnmower: Regularly maintain your lawnmower, including changing the oil, sharpening the blades, and cleaning the mower deck.

What if the surging persists after I’ve checked the common causes?

If the surging persists after you have checked the common causes, you may need to take your lawnmower to a qualified mechanic. There may be a more complex issue that requires professional attention.

The mechanic can diagnose the problem and recommend the best course of action to fix it.

What are some safety tips when working on a lawnmower?

It’s important to follow safety precautions when working on a lawnmower, as it can be dangerous.

  • Disconnect the spark plug: Before working on any part of the engine, disconnect the spark plug to prevent accidental starting.
  • Wear safety glasses: Protect your eyes from flying debris.
  • Work in a well-ventilated area: Avoid working on the lawnmower in a confined space.
  • Use appropriate tools: Use the correct tools for the job to avoid damaging the mower.
  • Never operate a lawnmower while under the influence of alcohol or drugs.

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