I have never fouled a plug in close to 10,000 miles. About 8500 miles was with the E50 (1-speed) and the rest was with the 2-speed Puch motor.
In fact, for about half of those miles I was using a surface gap spark plug. They have an extremely cold heat range rating. Cold heat range = easy plug fouling but I never even fouled the surface gap plug. Its ceramic insulator would be basically black, but it never failed. I use a synthetic oil (Royal Purple) mixed at 60:1