Comprehensive Guide: Why Is Smoke Coming Out of My Lawn Mower?

A well-functioning lawn mower is key to maintaining a beautiful and manicured lawn. However, when your lawn mower starts emitting smoke, it can be a cause for alarm and a sign that something is amiss. In this comprehensive guide, we will explore the various reasons why your lawn mower might be smoking, how to diagnose the problem, and the steps to take to perform necessary repairs or replacements. By understanding the potential causes and how to address them, you can ensure your lawn mower remains in optimal working condition and your lawn stays looking its best.

Lawn Mower

Causes of Lawn Mower Smoking

Lawn mowers are essential tools for maintaining a well-manicured lawn. However, they can sometimes emit smoke, which can be concerning for the owner. There are several reasons why a lawn mower might smoke, and understanding these causes can help identify the problem and fix it.

A. Dirty air filter

A clogged air filter reduces airflow and efficiency, causing the engine to work harder. This results in excess unburned fuel escaping, appearing as smoke.

  • Air filters should be regularly cleaned or replaced to ensure optimal engine performance.
  • Some lawn mowers have reusable filters that can be washed, while others require disposable filters.

B. Rich fuel mixture

If the carburetor is improperly adjusted or damaged, it can allow too much fuel into the combustion chamber, resulting in wasted unburned fuel as smoke.

  • A properly adjusted carburetor ensures the correct fuel-to-air ratio for efficient combustion.
  • A damaged carburetor may require repair or replacement.

C. Faulty spark plug

A bad spark plug cannot ignite the fuel properly, leading to unburned fuel escaping as smoke.

  • Spark plugs should be inspected and replaced regularly.
  • Using the wrong type of spark plug can also lead to inefficient combustion and smoking.

D. Blown head gasket

The head gasket seals the engine and allows for a proper fuel-air mixture. If damaged or blown, exhaust can enter the combustion chamber and exit as smoke.

  • A blown head gasket can cause significant damage to the engine.
  • Repairing or replacing a head gasket can be a challenging task and may require professional assistance.

Lawn Mower

Diagnosing the Problem

To determine the cause of smoke coming from a lawn mower, it is essential to perform a thorough inspection and diagnosis.

A. Check air filter

  • Replace the air filter if dirty.
  • Look for tears or damage that may impair its function.

B. Check spark plug

  • Replace the spark plug if fouled, damaged, or if the incorrect plug is installed.
  • Ensure the proper gap between the electrodes to facilitate efficient ignition.

C. Check for fuel leaks

  • Observe the carburetor and components for any cracked or damaged parts allowing excess fuel into the engine.
  • A fuel leak can cause a rich fuel mixture and smoking, as well as pose a fire hazard.

D. Check compression

  • Use a compression tester to check compression in each cylinder.
  • Low compression can indicate a blown head gasket or other engine issues.

Performing Repairs or Engine Replacement

Once the cause of the smoke has been identified, take the necessary steps to repair or replace the affected components.

A. Air filter, spark plug, or carburetor repair/replacement

  • Clean or replace the air filter as needed.
  • Replace the spark plug if it is fouled or damaged.
  • Adjust or replace the carburetor if it is causing a rich fuel mixture.

B. Head gasket replacement for minor damage

  • If the head gasket is damaged but not severely blown, it may be possible to replace it without replacing the entire engine.
  • Head gasket replacement is a complex task and may require professional assistance.

C. Complete engine replacement

For severe issues or a blown head gasket, the entire engine may need replacement.

  • Assess the cost of engine replacement versus purchasing a new lawn mower.
  • Consult a professional for advice and assistance with engine replacement.


A smoking lawn mower can be a cause for concern, but understanding the potential causes and performing a thorough diagnosis can help identify and resolve the problem. Regular maintenance, including cleaning or replacing the air filter, inspecting the spark plug, and checking the carburetor, can prevent many issues that lead to smoking. In cases where the head gasket is damaged or the engine has severe problems, seeking professional assistance is recommended to ensure a safe and effective repair or replacement. By addressing the underlying cause of the smoke, you can prolong the life of your lawn mower and maintain a healthy, well-kept lawn.


  • Nathan Collins

    Having spent years working in the landscaping industry, Nathan Collins has cultivated a wealth of knowledge about the natural world. He is committed to helping others appreciate the beauty in their backyards, whether it's through identifying rare rocks and minerals or crafting the perfect landscape.

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