This may actually be a repost - my apologies if it is - I've been gunna post it up for over 12 months now, can't recall if I have done so already, but I rediscovered the pics today.
Anyhow, going back to late 1997, I had my little DT125 racer running with a DT175 top end. The air cleaner fell off in practice, so cleaned out the carby, reattached the filter and went out for more practice.
Got a few laps in before it just died in the arse.
Pushed it back to the pits, and pulled the spark plug out to discover that the plug gap had closed up, and there was a tiny rectangular lump of something jammed down next to the porcelin.
Slapped a new plug in and it fired straight back up.
Raced the bike that weekend, and two more HEAVEN meets. Toward the end, it was clearly down on power, and a bit low on compression, but I never thought much of it - it had been flogged hard, and it wasn't even a fresh top end to begin with, so you gotta expect these things.
Anyhow, early last year, I got the ported 125 top end back from Uncle Lozza, so the 175 top end came off. This is what I found:
I think the only correct word is "oops".