Component Tests and General Diagnostics

1. Check the following items to see that electrodes are not burnt, and insulators are not broken, and how porcelain insulator is burnt.
- Broken insulators
- Wearing electrodes
- Deposited carbon
For cleaning, use a plug cleaner or wire brush. Clean porcelain insulator above shell as well.
- Damaged or broken gasket
- Burnt condition of porcelain insulator at spark gap Dark deposit of carbon indicates too rich a fuel mixture or extremely low air intake. Also, misfiring due to excessive spark gap is suspected.
White burn indicates too lean a fuel mixture or excessively advanced ignition timing. Also insufficient plug tightening is suspected.
2. Clean with a plug cleaner.
Use an air gun to remove dust deposited on plug threads.
3. Check plug gap using a plug gap gauge and adjust if it is not as specified.
Standard value: 1.0 - 1.1 mm (0.039 - 0.043 in.)