It’s important to remember that surface gap plugs operate at the temperature of the cylinder head. The center electrode area remains cold, and is unable to allow the combustion products to be burned off. In addition they typically require high energy discharge or CD ignition systems to fire across the carbon laden center insulator. Surface gap plugs have no specific heat rang as conventional plugs do, and only vary in their thread length and distance between center electrode and plug body’s ground surface. I prefer to not use them, as I have experienced a fair amount of misfiring when they were installed. They typically do not work with conventional magneto ignition systems. R.T.
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