CAUTION: Use the recommended spark plug. Refer to Technical data section of your manual. An incorrect spark plug can cause damage to the product.
Take the spark plug gently out of the socket. Remove any carbon or other foreign material lodged between the center and ground electrode with a steel brush, then let the spark plug dry.
A large gap puts a lot of stress on the ignition module and can cause short-circuiting.
Make sure the gap is correct before putting the spark plug back in place.
You can find the correct spark plug gap in your product's operator's manual.
If the electrodes are worn more than 50%, replace the spark plug.
The distance between electrodes and the type of spark plug are specified for every particular model in the trimmer user's manual.
Make sure the spark plug turns easily into the thread while screwing it back, and verify that is firmly screwed without over tight it.