Spark Plug: Testing and Inspection

Spark Plug Inspection





1. Inspect the electrodes and ceramic insulator for:
- Improper gap
- Oil-fouling
- Carbon deposits
- Cracked center electrode insulator

Burned or worn electrodes may be caused by:
- Lean fuel mixture
- Advanced ignition timing
- Loose spark plug
- Plug heat range too high
- Insufficient cooling

Fouled plug may be caused by:
- Rich fuel mixture
- Retarded ignition timing
- Oil in combustion chamber
- Incorrect spark plug gap
- Plug heat range too low
- Excessive idling/low speed running
- Faulty automatic choke (Carbureted engine)
- Clogged air cleaner element
- Deteriorated ignition coil or ignition wires








2. Replace the plug if the center electrode is rounded as shown.

3. Adjust the gap with a suitable gapping tool.

Electrode Gap: 1.0-1.1 mm (0.039-0.043 in.)

4. Screw the plugs into the cylinder head finger tight, then torque them to 18 Nm (1.8 kg-m, 13 lb-ft).

NOTE: Apply a small quantity of anti-seize compound to the plug threads before installing.