To help you ensure accurate spark plug installation first time, please follow DENSO’s specifications below:

Appearance: The insulator foot section and electrode section are covered with dried, soft black carbon.

Effects: Poor starting, misfiring, acceleration defect.

Cause: Repeated short-distance driving (driving with the engine cool), incorrect choking (overly rich air-fuel mixture), injection timing delay, plug heat range too high.

Appearance: The insulator section and electrode section are black and lustrous with wet oily deposits.

Effects: Poor starting and misfiring.

Cause: Oil leakage due to piston ring, cylinder, or valve guide wear (occurs easily to new engines and engines that have just been overhauled), high oil content in air-fuel mixture (2-stroke engines).

Appearance: The insulator leg section is scorched and extremely white with small black deposits. Rapid electrode wear.

Effects: Loss of power when running at high speed or under high load.

Cause: Spark plug incorrectly tightened, engine cooling problem, ignition timing too early, spark plug heat range too low, severely abnormal combustion.

Appearance: The centre electrode or ground electrode is melted or scorched. There are spots on the insulator leg section and deposits of aluminium or other metal powder.

Effects: Power loss due to engine damage.

Cause: Often this is due to overheating; pre-ignition is a phenomenon in which combustion occurs before ignition. The plug heat range is too low, the injection timing is too advanced, etc.

Appearance: The insulator leg section is cracked or broken.

Effects: Misfiring

Cause: Severely abnormal combustion, lack of attention to gap adjustment.