Why Is My John Deere Lawn Mower Surging?

There’s nothing more frustrating than trying to maintain your beautiful lawn, only to have your John Deere lawnmower suddenly start surging, making a smooth cut impossible. This unpredictable behavior can leave you feeling baffled and defeated. But don’t worry, understanding the reasons behind this issue is the first step towards a smooth-running lawnmower. This comprehensive guide will delve into the common culprits behind your John Deere lawnmower surging, providing you with actionable solutions to get your mower back in tip-top shape.

A brief overview

Lawn mower surging is usually caused by issues with the fuel system, ignition system, or air intake system. It could be a clogged air filter, dirty carburetor, or a faulty spark plug. By understanding the possible causes and troubleshooting steps, you can identify and fix the problem effectively.

Fuel System Problems: The Root of the Issue

The fuel system plays a crucial role in your lawnmower’s performance. When the fuel delivery is inconsistent, it can lead to surging. Let’s examine some common fuel system issues:

1. Clogged Fuel Filter:

A clogged fuel filter restricts the flow of fuel to the engine, causing fuel starvation and uneven combustion. This can result in your lawnmower surging.

How to Check and Replace:

  • Locate the fuel filter (usually a small cylindrical object near the fuel tank).
  • Disconnect the fuel lines leading to and from the filter.
  • Carefully remove the filter and inspect it for debris.
  • Replace the filter with a new one of the correct size and type.

2. Dirty or Clogged Carburetor:

The carburetor mixes air and fuel before it enters the engine. If it’s dirty or clogged, the fuel-air mixture becomes unbalanced, leading to surging.

Troubleshooting a Dirty Carburetor:

  • Clean the carburetor:
    • Remove the carburetor from the engine.
    • Carefully disassemble it and clean all parts with carburetor cleaner.
    • Soak the carburetor in a solution of carburetor cleaner and water for a few hours.
    • Rinse the carburetor thoroughly with clean water.
    • Reassemble the carburetor and reinstall it on the engine.
  • Rebuild the carburetor:
    • If the carburetor is severely worn or damaged, consider rebuilding it with a rebuild kit. This involves replacing worn-out parts like gaskets, seals, and jets.

3. Fuel Line Problems:

Cracked, kinked, or clogged fuel lines can obstruct the fuel flow to the carburetor, resulting in surging.

Diagnosing and Replacing Fuel Lines:

  • Visual inspection: Inspect the fuel lines for cracks, kinks, or leaks.
  • Pressure test: Use a fuel pressure tester to check if the fuel line is delivering adequate pressure to the carburetor.
  • Replacement: If you find any issues, replace the affected fuel lines with new ones of the correct size and material.

Ignition System Malfunctions

The ignition system ensures that the spark plug ignites the fuel-air mixture at the right time. A malfunctioning ignition system can also lead to surging.

1. Worn or Fouled Spark Plug:

A worn or fouled spark plug cannot generate a strong enough spark to ignite the fuel-air mixture efficiently. This causes inconsistent combustion and surging.

Checking and Replacing the Spark Plug:

  • Remove the spark plug: Use a spark plug wrench to remove the spark plug from the engine.
  • Inspection: Inspect the spark plug for signs of wear, fouling (carbon buildup), or damage.
  • Replacement: If the spark plug is worn, fouled, or damaged, replace it with a new one of the correct type and gap.

2. Faulty Ignition Coil:

The ignition coil provides the high voltage required to spark the spark plug. If the ignition coil malfunctions, it will not provide the necessary voltage, leading to weak sparks and surging.

Testing the Ignition Coil:

  • Continuity test: Use a multimeter to check for continuity between the ignition coil’s terminals.
  • Resistance test: Check the resistance of the ignition coil’s primary and secondary windings.
  • Replacement: If the ignition coil fails any of these tests, replace it with a new one.

Air Intake System Issues

The air intake system supplies the engine with fresh air for combustion. Issues in this system can disrupt the fuel-air ratio, resulting in surging.

1. Clogged Air Filter:

A clogged air filter restricts airflow to the engine, reducing the amount of oxygen available for combustion. This can cause a lean fuel-air mixture and lead to surging.

Inspecting and Replacing the Air Filter:

  • Location: The air filter is usually located near the carburetor.
  • Inspection: Remove the air filter and inspect it for dirt, debris, or blockage.
  • Replacement: If the air filter is dirty or clogged, replace it with a new one.

2. Leaky Intake Manifold:

A leaky intake manifold allows unfiltered air to enter the engine, disrupting the fuel-air mixture and causing surging.

Diagnosing and Repairing Leaks:

  • Visual inspection: Check the intake manifold for cracks or leaks.
  • Pressure test: Use an air pressure tester to pressurize the intake manifold and check for leaks.
  • Repair: If you find any leaks, repair them using sealant or replace the damaged manifold.

Other Possible Causes

While the above are the most common culprits, other factors can contribute to surging:

  • Fuel Quality: Using old or contaminated fuel can lead to inconsistent combustion and surging.
  • Engine Tune-Up: A poorly tuned engine may exhibit surging due to improper settings for the carburetor or ignition system.
  • Incorrect Throttle Cable Adjustment: A misadjusted throttle cable can cause the throttle to stick or respond inconsistently, leading to surging.

Tips for Preventing Surging

  • Regular Maintenance: Regularly inspect and clean your lawnmower’s fuel system, air intake system, and ignition system to prevent problems and maintain optimal performance.
  • Use Fresh Fuel: Always use fresh, high-quality fuel and avoid storing fuel for extended periods.
  • Store Properly: Properly store your John Deere lawnmower during the off-season to prevent fuel degradation and carburetor issues.

When to Seek Professional Help

If you’ve tried the troubleshooting steps outlined above and your John Deere lawnmower still surges, it’s best to consult a qualified mechanic. They can diagnose the problem accurately and provide the necessary repairs.


Surging in your John Deere lawnmower can be a frustrating experience, but armed with knowledge and troubleshooting techniques, you can confidently address the issue. By carefully inspecting and cleaning the fuel system, ignition system, and air intake system, you can identify and fix the root cause of the surging. Remember, preventative maintenance and regular checks are key to enjoying a smooth-running and trouble-free mowing experience.

Frequently Asked Questions

Q1: What does “surging” mean in terms of a lawnmower?

“Surging” refers to a lawnmower that is not running smoothly. It may accelerate suddenly, then slow down or stop completely, and then repeat this process. This can be caused by a variety of factors, such as a clogged air filter, a faulty carburetor, or a problem with the fuel system.

It’s important to address surging promptly as it can damage the engine and lead to other problems. If your John Deere lawnmower is surging, it’s best to stop using it immediately and investigate the cause of the issue.

Q2: What are the common causes of lawnmower surging?

There are several common causes of lawnmower surging. One possibility is a clogged air filter, which restricts airflow to the engine and can cause it to run erratically. Another culprit could be a faulty carburetor, which is responsible for mixing air and fuel in the correct proportions. A clogged carburetor can cause surging by delivering too much or too little fuel to the engine.

Problems with the fuel system, such as a dirty fuel tank or a blocked fuel line, can also lead to surging. Additionally, a faulty ignition system, including spark plugs or ignition coils, can cause the engine to misfire and surge.

Q3: How can I check for a clogged air filter?

Checking for a clogged air filter is a simple process. First, locate the air filter, which is usually a rectangular box with a cover. Remove the cover and carefully inspect the filter element. If it appears dirty or clogged with debris, it needs to be replaced.

A clean air filter is essential for proper engine performance. A clogged filter restricts airflow to the engine, leading to reduced power and increased fuel consumption. It can also cause the engine to overheat and surge. Regularly cleaning or replacing the air filter helps ensure optimal performance and longevity of your John Deere lawnmower.

Q4: How can I clean or replace the carburetor?

Cleaning or replacing a carburetor can be a more involved process. You can attempt to clean the carburetor yourself using a carburetor cleaning kit and following the instructions provided. This involves disassembling the carburetor, cleaning the various components, and then reassembling it.

However, if the carburetor is severely damaged or you are not comfortable with this process, it’s recommended to take your lawnmower to a qualified mechanic for professional repair. A damaged or malfunctioning carburetor can lead to engine surging, poor fuel economy, and reduced power.

Q5: What should I do if I suspect a fuel system problem?

If you suspect a fuel system problem, you should start by checking the fuel tank for any debris or water. If necessary, clean the fuel tank and refill it with fresh fuel. You should also inspect the fuel lines for any kinks or blockages.

If you find any issues with the fuel lines, they should be repaired or replaced. It’s also advisable to drain the old fuel from the carburetor and replace it with fresh fuel. A clean fuel system ensures that the engine receives a consistent supply of fuel, leading to optimal performance and preventing engine problems.

Q6: How can I check the ignition system?

Checking the ignition system involves inspecting the spark plugs and ignition coils. The spark plugs should be removed and inspected for signs of wear or damage. The gap between the electrodes should be checked and adjusted if necessary.

The ignition coils should also be inspected for any cracks or other damage. If any of these components are found to be faulty, they should be replaced. A faulty ignition system can cause the engine to misfire, resulting in surging and reduced power.

Q7: What are some other potential causes of lawnmower surging?

While the most common causes of lawnmower surging are those related to the air filter, carburetor, and fuel system, other factors can also contribute to the problem. For example, a loose or faulty connection in the electrical system can cause intermittent issues.

Also, a worn-out or damaged governor can cause the engine to run erratically. If you have ruled out the most common causes and are still experiencing surging, it’s a good idea to seek professional help to diagnose and repair the issue.

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