You might be right, It's not too bad Norm, Old type Race pistons, 10 thou gap. I tried 7 thou and locked it up on the M4 Playing with a HondaKwaki I am running Champion N5, Now gone over to N9yc, Don't really want to go any hotter, In case it holes a piston, Any colder, stops in 20 miles.Is the engine using any oil Bill? Could you be leaning it off to make the plugs hot enough to keep them clean of oil? ( I think you mentioned that possibility in a post above) What happens with the next grade hotter plug?
Cheers Bill.