The last time I ran this engine, it ran just fine. No problem tuning it. Lots of power. When I opened it up today, I see this mean gouge down the side of the piston and I'm like, "What's up with this?"

What are you thoughts on this and how did it get this way? Why is it still running okay? What could happen if I continue to run it?

I'm assuming I can't continue running it like this ... or can I?