half moon cookie plug

ive had some problems with fouling plugs with my 96/91 CR125, ive got the main jet just about perfect,needle seems to be perfect, and im pretty sure that the pilot was too big because the fouling only occured when i would slowly ride my bike back and put it away. Well anyways i went from a 58 pilot to a 55 and just idleing it it seemed alot crisper off the bottom, but after i rode it i did a chop test with the throttle just barely open, and the plug was half black with other half being stark white. ???? it seems to be running good but i havent been able to ride it much more just wanna know why my plug looks like a half moon cookie

I was tempted, but it didnt smell quite as appetizing as it looked :) ....anyways seems to be fine now j/w hat causes the plug to sometimes look like that.