It was a couple months ago and looking over my previous post, I'm not sure exactly what I did or if it was actually .8mm. Doesn't seem that is what I would have done, but instead I would have adjusted the gap somewhere in between the .6mm and .7mm. Sorry I can't remember exactly, but I can say that the plug, inside the tailpipe, as well as the OS2 sensor, were all carbon covered.
In my case, the starting issue I was having and the carbon buildup was due to water in the gas tank. According to my mechanic, he stated that there was enough water in the tank to cause my starting issue, as well as the cause of carbon buildup on the plug, OS2 sensor and tailpipe.
After being repaired, so far, my UTV is starting and running great since the water was removed and the tank filled with fresh gas. I haven't checked the plug or sensor as of yet to see if carbon has reappeared, since the UTV was repaired and now running good.
Are you having other issues, such as hard starts, stalling etc.,?