Why Does My Lawn Mower Surge? (Issues, Problems & Factors)

Lawnmowers are indispensable tools for maintaining a well-manicured yard, allowing us to trim grass and keep our outdoor spaces tidy effortlessly.

However, these machines sometimes encounter a frustrating issue known as “mower surging.”

This phenomenon, characterized by irregular fluctuations in engine speed, can hinder the mower’s performance and make lawn care tasks more challenging.

In this article, we write about the causes of why does my lawn mower surges, exploring the intricacies of fuel systems, air intake systems, and ignition systems. And other factors that contribute to mower surging.

By perceiving the root causes, you’ll be equipped with the knowledge to troubleshoot and resolve this issue, ensuring a smoother mowing experience.

Why Does My Lawn Mower Surge?

Lawn mower surge refers to the irregular or fluctuating engine speed that occurs during operation.

It is characterized by the engine revving up and down, causing a noticeable variation in the mower’s cutting power and overall performance.

Mower surge involves recognizing its symptoms and comprehending its impact on the mower’s operation.

Defining Mower Surge and Its Symptoms

Mower surge refers to the inconsistent and erratic behavior exhibited by a lawn mower’s engine during operation. It is characterized by fluctuating engine speed, causing the mower to surge forward or decelerate abruptly.

This phenomenon disrupts the smooth and steady cutting process, leading to an uneven and unsightly lawn appearance.

When a mower surges, you may notice sudden accelerations or decelerations, irregular engine sounds, and intermittent power loss.

These symptoms can make mowing difficult, hinder productivity, and potentially damage the mower if not addressed promptly.

Perception of the nature of mower surges is essential in diagnosing the underlying causes and implementing the appropriate solutions.

Explaining the impact of surgeon mower performance

When a lawn mower experiences surging, it can have a significant impact on its overall performance. The surging creates an inconsistent flow of power to the engine, causing the mower to rev up and down irregularly.

This fluctuation in power output leads to an uneven cutting pattern, resulting in an untidy lawn appearance.

Additionally, the surging can make the mower difficult to control, leading to a bumpy and uneven mowing experience.

Furthermore, the constant variation in engine speed can put additional stress on various components, potentially leading to premature wear and tear.

To ensure optimal performance and a well-maintained lawn, addressing the issue of surge promptly is crucial.

Fuel System Issues

The fuel system plays a crucial role in the proper functioning of a lawn mower. When it comes to mower surging, fuel system problems are often the culprits.

This section will delve into three common fuel system issues that can cause surging: clogged fuel filters, dirty carburetor, and fuel line problems.

(I) Clogged Fuel Filter

The fuel filter plays a crucial role in keeping your lawn mower’s engine running smoothly. Its primary function is to prevent dirt, debris, and impurities from reaching the engine and causing damage.

However, over time, the fuel filter can become clogged, hindering the proper flow of fuel. Signs of a clogged fuel filter include engine surging, stalling, or difficulty starting.

To address this issue, you can start by locating the fuel filter, which is usually situated between the fuel tank and the carburetor.

Cleaning or replacing the fuel filter is the recommended solution. Regularly inspecting and maintaining the fuel filter will help ensure optimal engine performance and prevent surging.

(II) Dirty Carburetor

The carburetor plays a crucial role in the operation of a lawn mower. It is responsible for mixing air and fuel in the correct ratio before it enters the engine for combustion.

However, over time, the carburetor can become dirty due to the accumulation of debris, dirt, or old fuel residues.

A dirty carburetor can lead to several issues, including mower surging. It can disrupt the proper air-fuel mixture, causing inconsistent engine performance and fluctuations in speed.

Additionally, a dirty carburetor may result in poor fuel efficiency and difficulty in starting the mower. To address this problem, you can clean the carburetor using carburetor cleaner and a soft brush.

Disassembling the carburetor and soaking its parts in the cleaner can effectively remove built-up deposits.

If cleaning doesn’t resolve the issue, it may be necessary to replace the carburetor with a new one to restore optimal functioning and eliminate surging.

(III) Fuel Line Problems

Fuel line problems can contribute to surging issues in lawn mowers. Identifying fuel line blockages or leaks is crucial in troubleshooting this aspect.

Blockages can occur due to debris or sediment buildup, obstructing the flow of fuel to the engine.

On the other hand, leaks in the fuel line can lead to decreased fuel pressure, resulting in erratic engine performance and surging.

To address fuel line problems, start by visually inspecting the fuel line for any visible leaks or signs of damage.

Next, remove the fuel line and check for blockages by blowing compressed air through it or using a small brush to remove debris. If leaks are detected, replacing the fuel line with a new one is recommended.

Proper maintenance and regular inspections of the fuel line will help prevent surging caused by fuel delivery issues.

Air Intake System Problems

The air intake system of a lawn mower plays a crucial role in its performance. Two common issues that can cause surging are a dirty air filter and a faulty choke.

Problem 1: Dirty Air Filter

A clean air filter is essential for proper airflow to the engine. When the air filter becomes clogged with dirt, grass clippings, or debris, it restricts the airflow, resulting in a rich fuel mixture and potential surging.

Symptoms of a clogged air filter include difficulty starting the mower, reduced power, and erratic engine performance.

To address this problem, start by locating the air filter housing and removing the filter. Inspect the filter for dirt and debris, and if necessary, clean it using compressed air or by tapping it gently to remove loose particles.

If the air filter is excessively dirty or damaged, it’s recommended to replace it with a new one for optimal performance.

Problem 2: Faulty Choke

The choke plays a vital role in starting the mower by regulating the air-to-fuel ratio during cold starts. A faulty choke can cause the engine to run too rich or too lean, resulting in surging.

Symptoms of a faulty choke include difficulty starting the engine, stalling, or rough idling.

To troubleshoot choke-related issues, inspect the choke mechanism for any visible damage or misalignment. Ensure that the choke is closing properly during cold starts and opening fully when the engine warms up.

Cleaning the choke assembly and lubricating any moving parts can also help resolve minor issues. If the choke is severely damaged, it may need to be replaced to restore proper functionality.

Ignition System Malfunctions

The ignition system plays a critical role in the operation of a lawn mower’s engine. Two components that can contribute to surging issues are spark plug problems and a faulty ignition coil.

A. Spark Plug Issues

The spark plug is a small but crucial part of the ignition system. It ignites the fuel-air mixture in the combustion chamber, ensuring proper engine operation.

Common spark plug problems that can lead to surging include fouling, wear, or improper gap.

To address spark plug issues, start by removing the spark plug using a spark plug socket and inspecting it for signs of fouling, such as carbon buildup or oil deposits. If fouling is present, clean the spark plug using a wire brush and a suitable cleaner.

Check the spark plug electrode gap and adjust it to the manufacturer’s specifications using a gap tool. If the spark plug is excessively worn or damaged, it’s recommended to replace it with a new one.

B. Faulty Ignition Coil

The ignition coil is responsible for generating the high voltage needed to create the spark at the spark plug.

A faulty ignition coil can lead to weak or inconsistent spark production, resulting in surging or engine misfires.

To diagnose a faulty ignition coil, start by checking for visible signs of damage, such as cracks or corrosion.

Using a multimeter, measure the resistance across the ignition coil terminals according to the manufacturer’s specifications.

If the resistance readings are outside the recommended range, it indicates a defective ignition coil that needs replacement.

Ensure to disconnect the spark plug wire and any electrical connections before replacing the ignition coil.

Engine-related Factors

The proper functioning of the engine is crucial for a lawn mower’s performance. Several engine-related factors can contribute to mower surging.

In this section, we will explore three key factors: engine overload, low engine oil level, and old or contaminated fuel.

Factor 1: Engine Overload

Overloading the engine of your lawn mower can lead to detrimental effects, including surging.

When the engine is overwhelmed with an excessive workload, it struggles to maintain a consistent speed, resulting in fluctuations and surging.

To prevent engine overload and subsequent surging, consider the following tips:

  1. Avoid cutting grass that is too tall or dense: Mowing grass that exceeds the recommended height or density puts excessive strain on the engine. Gradually reduce the grass height by mowing more frequently or using a higher cutting deck setting.
  2. Do not rush: Pushing the mower at an unnaturally fast pace increases the workload on the engine. Maintain a steady and moderate speed while mowing to prevent overloading.
  3. Clear the cutting path: Before mowing, remove any debris, rocks, or large objects from the lawn to prevent the engine from straining while cutting through them.
  4. Use appropriate mower size: Ensure that you are using a mower with an engine capacity suitable for your lawn’s size. Using an underpowered mower for a large lawn may cause the engine to overload more frequently.

Factor 2: Low Engine Oil Level

Maintaining proper engine oil levels is vital for the smooth operation of your lawn mower. Insufficient oil can lead to various problems, including engine surging.

Here’s why proper oil levels are essential and how you can ensure they are maintained:

  1. Importance of proper engine oil levels: Engine oil lubricates the internal components of the mower’s engine, reducing friction and heat. Insufficient oil restricts the lubrication process, leading to increased friction, overheating, and eventually, surging.
  2. Consequences of low oil levels: When the oil level is too low, the engine lacks the necessary lubrication, causing increased wear on the moving parts. This can result in decreased performance, increased fuel consumption, overheating, and ultimately, engine damage.
  3. Checking and adding oil: To maintain proper oil levels, follow these steps:
  • Consult your mower’s manual to locate the oil fill cap or dipstick.
  • Park the mower on a level surface and let the engine cool down.
  • Remove the oil fill cap or dipstick and wipe it clean.
  • Insert the dipstick back into the oil fill hole without screwing it in and then remove it again.
  • Check the oil level on the dipstick. If it’s below the recommended level, add oil as per the manufacturer’s instructions.
  • Avoid overfilling the oil, as it can also cause performance issues.
  • By regularly checking and maintaining the proper engine oil level, you can promote smooth operation and minimize the risk of surging.

Factor 3: Old Or Contaminated Fuel

The quality of fuel used in your lawn mower plays a significant role in its performance. Using old or contaminated fuel can lead to engine problems, including surging.

Let’s explore the effects of old or contaminated fuel and how to address this issue:

  1. Effects of old or contaminated fuel: Over time, fuel can degrade, oxidize, or become contaminated with impurities. When old or contaminated fuel is used, it can clog the fuel system, affecting the proper functioning of the engine. This can result in surging, sputtering, or even engine stalling.
  2. Draining and refilling the fuel tank: To address the issue of old or contaminated fuel, follow these steps:
  • Turn off the engine and let it cool down.
  • Locate the fuel tank on your lawn mower and place a suitable container beneath it to catch the fuel.
  • Remove the fuel cap and carefully drain the old fuel into the container.
  • Check for any signs of contamination, such as water or debris, in the drained fuel.
  • Dispose of the old fuel properly according to local regulations.
  • Refill the fuel tank with fresh, high-quality gasoline that is recommended for your mower.
  • Ensure the fuel cap is securely tightened.

Other Contributing Factors

While fuel system issues, air intake system problems, and ignition system malfunctions are common culprits of lawn mower surging, other factors can also contribute to this problem.

Understanding these additional factors will help you diagnose and resolve surging issues effectively.

  • Blade Problems

Blade problems, such as dullness or imbalance, can significantly contribute to mower surging. Dull blades struggle to cut grass cleanly, causing the engine to work harder and potentially surge.

Similarly, unbalanced blades can create uneven cutting patterns, leading to imbalanced engine performance.

To address these issues, regular blade maintenance is essential. Sharpening dull blades and ensuring proper balance can restore optimal cutting performance and prevent surging.

If the blades are severely damaged or cannot be balanced, replacing them with new ones is recommended for smooth and efficient mowing.

  • Transmission Troubles

Transmission-related problems can significantly impact the performance of your lawn mower. A faulty transmission can lead to surging and erratic movements. It may cause the mower to jerk, stall, or have difficulty changing gears.

To diagnose transmission issues, observe any unusual noises, difficulty in engaging gears, or a loss of power. If a problem is detected, check the transmission fluid level and condition.

Low fluid levels or dirty fluid can contribute to transmission problems. Resolving transmission issues often involves cleaning or replacing the transmission fluid, adjusting the linkage, or seeking professional repair.

  • Mechanical Wear and Tear

Over time, general wear and tear can take a toll on your lawn mower and contribute to surging. Worn-out components such as belts, bearings, and pulleys can lead to irregular engine operation and cause surging.

To prevent these mechanical problems, regular maintenance is crucial. Lubricate moving parts, replace worn-out belts and bearings, and ensure pulleys are properly aligned.

Additionally, keep an eye on the condition of the drive system and inspect for any signs of damage or excessive wear.

By addressing mechanical wear and tear promptly, you can maintain a smoother and more reliable operation of your lawn mower.


Clogged fuel filters and dirty carburetors often disrupt the fuel system, while dirty air filters and faulty chokes affect the air intake system.

Spark plug issues and faulty ignition coils impact the ignition system, and engine-related factors such as overload, low oil levels, and old or contaminated fuel contribute to surging.

Blade problems, transmission troubles, and mechanical wear and tear also play a role. Regular maintenance is crucial in preventing these issues.

By troubleshooting and addressing these causes promptly, mower owners can maintain optimal performance and avoid the frustrating surging problem altogether.


Why does my lawn mower surge while in use?

Lawnmowers may surge due to various reasons such as clogged fuel filters, dirty carburetors, or issues with the air intake system. Other factors like spark plug problems, engine overload, or low oil levels can also contribute to surging.

Can a surging lawn mower damage the engine?

Yes, continuous surging can put stress on the engine, leading to potential damage. It’s important to identify and address the underlying causes of surging promptly to prevent any long-term damage to the mower’s engine.

How often should I perform maintenance on my lawn mower to prevent surging?

Regular maintenance is key to preventing surging issues. It is recommended to perform maintenance tasks such as cleaning or replacing filters, inspecting spark plugs, checking oil levels, and servicing mechanical components at least once a year or as per the manufacturer’s guidelines.

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