yeah that would suggest excessive overheating though. a few days ago I started leaning out the motor and tuning it for performance running my 25% race fuel always keepin an eye on temps as it is now fully broke in. I'm letting it run at between 100-110c as apposed to 80c for break in running 16%. no dead plugs after a few tanks so heat isnt the culprit, that I'm sure of.
I'm pretty sure ed's onto somethin, as it happens regardless of temps. I've never seen a plug with melted or even grey wire as I alway run just below optimum, I simply dont let my motors run that hot.