My Petrol Lawnmower is blowing black smoke

If your petrol lawnmower is producing black smoke from the exhaust, the engine is typically running with too much fuel and not enough air. In most cases, this is caused by a dirty or blocked air filter restricting airflow to the engine.

This guide explains how to inspect and clean or replace the air filter.

Table of Contents

1. Common Cause of Black Smoke

2. Accessing the Air Filter

3. Sponge Air Filter

4. Paper Air Filter

Common Cause of Black Smoke

Black exhaust smoke is usually a sign that the engine is running rich, meaning the fuel-to-air ratio contains too much fuel.

The most common cause is a dirty air filter that restricts airflow into the engine.

Other symptoms may include:

• Reduced engine performance

• Increased fuel consumption

• Rough running

• Difficulty starting

Before investigating further, inspect the air filter and clean or replace it as necessary.

Accessing the Air Filter

Step 1 – Locate the Air Filter Cover

The air filter is typically housed behind a cover mounted on the side of the engine.

Depending on your model, the cover may be secured by:

• A clip-on cover, or

• A retaining screw

Step 2 – Remove the Cover

Carefully remove the cover and take out the air filter element.

Inspect the filter to determine whether it is a sponge filter or a paper filter.

Sponge Air Filter

A clean sponge air filter is generally yellow or grey in colour.

Inspect the Filter

Check the filter for:

• Dirt

• Grass debris

• Oil contamination

• Damage

Cleaning the Filter

1. Wash the sponge filter in warm soapy water.

2. Rinse thoroughly.

3. Allow the filter to air dry completely.

4. Reinstall the filter and refit the cover.

Important: Never reinstall a wet air filter, as this can affect engine performance.

Paper Air Filter

A clean paper air filter is typically white or off-white in colour.

Inspect the Filter

Check for:

• Dirt build-up

• Tears or damage

• Oil contamination

• Heavy discolouration

Replacing the Filter

Paper air filters cannot be effectively cleaned.

If the filter is dirty, damaged, or heavily discoloured, it should be replaced with a new filter.

Once replaced, reinstall the air filter cover securely.