I am using a Victor 383 intake with a one inch 4 hole spacer, Demon RS carb with 1.50 venturi/1.75 base plate with an annular booster. I should have clarified the plugs are all from #1 on three different passes and were new before the pass.

There is very little carbon build up on the interior of plug where the porcelain is. When I look at the plugs under the scope you can see the black specs are only on one side of the plug. If the specks were coming from the interior would they be more uniform around the porcelain?

I guess I was thinking about the heat on the threads backwards, as I thought with it only impacting the top thread the plug was not too hot but maybe too cold, and is one of the reasons I posted.
It is the same for me with the strap, I have to remember it goes from the tip back, so when it is at the bottom close to the ring there is plenty of heat there. When I look inside the plug with the scope you can see where the heat has actually penetrated down inside the plug where the strap is attached.