How to test the spark plug

This guide explains how to check whether the spark plug on your machine is working correctly. If your engine will not start, the spark plug is one of the first components to inspect.

Table of Contents

1. Cleaning the Spark Plug
2. Tools Needed
3. How to Test the Spark Plug
4. Interpreting the Results
5. What to Do Next

Cleaning the Spark Plug

Before testing, inspect the spark plug for dirt or carbon build-up.

A dirty spark plug can prevent the engine from sparking correctly.

To clean it:

• Use a wire brush to remove carbon deposits
• Or wipe gently with a cloth lightly dabbed in petrol

Ensure the tip of the spark plug is clean before proceeding.

Tools Needed

• Spark plug wrench
  

How to Test the Spark Plug

Step 1 – Prepare the Area

Carry out the test in a shaded area so the spark is easier to see.

Step 2 – Remove the Spark Plug

1. Pull off the spark plug cap (thick black ignition cable).
2. Using a spark plug wrench, unscrew the spark plug anti-clockwise.
3. Remove it carefully from the engine.

Step 3 – Reattach to the Lead

• Insert the spark plug back into the cap/cable
• Allow it to hang securely from the lead

Step 4 – Earth the Spark Plug

• Press the metal threaded section of the spark plug firmly against a clean metal part of the engine
• This creates an earth connection for the test

Step 5 – Perform the Test

While holding the spark plug against the engine:

1. Hold down the start/stop lever on the handle
2. Pull the starter cord as if starting the engine

Interpreting the Results

Watch the tip of the spark plug closely:

• Bright white spark visible: Spark plug is working correctly
• No spark visible: Spark plug or ignition system may be faulty

What to Do Next

If the spark plug is not the cause of the issue, check the following:

• Fuel is fresh (less than 30 days old)
• Engine oil is at the correct level
• Air filter is clean and dry
• Starter cable is correctly tensioned

If No Spark Is Detected

If the spark plug does not produce a spark even after cleaning:

• The spark plug may need replacing
• If a replacement plug also does not spark, the ignition coil may be faulty

In this case, further technical support or repair may be required.