Oh Tiny Noooooooooo! I am so sorry to hear that. I was really rooting for you with that way cool Honda 250. I wish I was closer so I could come look at it with you after the meet to do an autopsy. Thanks for the video post. Awesome sounding 250cc engine until the extra noises started.
I think I may have had a crater in #4 piston before I left home,,from when I burned a plug earth strap during a sorting run, making that piston the sacrificial lamb ?
I sort of hope there will be a hole in 2 or 3 as well when I pull the head (damn near impossible to get those plugs out) , although it is not running lean,,it gets a failrly hot thing happening in the combustion chamber.
Although I have an EGT gauge , i decided not to fit it to the bike,,'cos they slow you down,,lol