My Petrol Hedge Trimmer is not running correctly

Spark Plug Check

If your petrol hedge trimmer is difficult to start, runs poorly, or will not start at all, checking the spark plug is an important diagnostic step. The spark plug generates the spark required to ignite the fuel mixture within the engine.

Table of Contents

Tools Required

1. Removing the Spark Plug
2. Checking the Condition of the Spark Plug
3. Testing the Spark Plug for a Spark
4. Testing with a Different Spark Plug
5. Reinstalling the Spark Plug

Tools Required

• Spark plug spanner/wrench 
• Wire brush (recommended)
• Clean cloth
• Petrol (for cleaning, if required)

1. Removing the Spark Plug

Step 1

Remove the spark plug cap (also known as the high-tension lead). This is the thick black rubber cap connected to the spark plug.

Step 2

Using a spark plug spanner, carefully turn the spark plug anti-clockwise until it can be removed from the engine.

Note: The spark plug may be tight and require some force to loosen.

2. Checking the Condition of the Spark Plug

Inspect the spark plug for signs of carbon build-up, dirt, or damage.

A spark plug covered in carbon deposits may not produce a sufficient spark to start the engine.

Cleaning the Spark Plug

If the spark plug is dirty:

1. Clean the electrode and threaded area using a wire brush.
2. Alternatively, wipe the spark plug with a clean cloth lightly dampened with petrol.
3. Ensure the spark plug is dry before testing or reinstalling.

3. Testing the Spark Plug for a Spark

Step 1

Remove and clean the spark plug as described above.

Step 2

Reconnect the spark plug to the spark plug cap.

Step 3

Position the threaded section of the spark plug against a clean metal part of the hedge trimmer to create an earth connection.

Step 4

Ensure the Start/Stop switch is in the START position.

Step 5

Move to a shaded area where the spark can be seen more clearly.

Step 6

Pull the starter cord firmly while observing the tip of the spark plug.

Result

• A faint white or blue flash indicates that the spark plug is producing a spark and is likely functioning correctly.
• No visible spark may indicate a faulty spark plug or an ignition system fault.

Important Safety Warning: Hold the spark plug using insulated materials and keep hands clear of the electrode during testing to avoid electric shock.

4. Testing with a Different Spark Plug

If available, remove a known working spark plug from another petrol-powered machine.

Step 1

Connect the working spark plug to your hedge trimmer's spark plug cap.

Step 2

Repeat the spark test procedure outlined above.

Results

• If the replacement spark plug produces a spark, your original spark plug is likely faulty and should be replaced.
• If neither spark plug produces a spark, the fault may lie within the ignition system, such as the ignition coil.

In this case, further inspection or replacement of the ignition coil may be required.

5. Reinstalling the Spark Plug

Once testing and cleaning have been completed:

Step 1

Carefully screw the spark plug into the engine by hand to avoid cross-threading.

Step 2

Tighten the spark plug securely using the spark plug spanner.

Step 3

Reconnect the spark plug cap, ensuring it is fully seated and securely attached.