I have always like NJK plugs for my bikes. Two stroke plugs can be pulled and 'wire brushed' off and reused many. Plugs are so cheap and with unleaded fuel on 4 stroke engines a plug hardly never-ever has to be changed: Bikes maybe at 25-50,000 miles and passenger vehicles maybe at 100,000 miles. Going to a 'colder' plug for BAJA type events where the throttle is held open at high vehicle/ engine speeds is much safer than a 'hotter' plug used stock for general use. Two stroke engines are really affected by heat range-not so much 4 strokes. When I raced semi-pro dirt/ desert/ ISDT type events, BAJA and hare & hound, European scramble events, a person had to learn quickly about heat ranges. Seoul, I always look at what plug comes with the scooter/ motorcycle and know from experience that in most cases the MFG's know what they are doing. The computer will retard the Ign timing to prevent the knock. I have forced these plugs to work by running crazy hot Accell 60K coils but the performance was actually hindered because the lack of a conventional plugs chamber forced random flame front ignition points inside the combustion chamber that simulated Pre Detonation.Ĭomputer controlled engines w/ Knock sensors suffer most. The engine is designed differently period. They have that flame front 'chamber' built into the cylinder head, and piston.

The engines these plugs are designed for are designed for the plugs. Gap less plugs have no heat rating because there is no chamber to create the flame front.

The smaller that chamber the hotter the plug rating. The insulator is there because when a plug fires, the fuel/air mix INSIDE the insulators chamber is what ignites, and starts the flame front. Heat range is determined by the length of the electrode's insulator. The reason those plugs misfire in conventional engines is directly related to your question to Porkie.

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