Yeah, you can run bit more compression on something that doesn't spin out as much. Combination of lots of RPM's and probably a hot spot etc caused it to start detonation. Oh and Steve hasn't ridden that 103 in almost year now... what the heck? Anyways, back off the timing a bit more.. probably 1.0mm btdc, run premium petrol. I run conservative timing around 1.0 to 1.1 btdc on 50cc kit that would jump above 14,000 rpm and still ended up popping a hole in the piston, I switched to a forged wiseco piston in hopes of reducing the chance of that happening again. Other possibility that might help is weld up that decomp hole and reface the head down. Oh and make sure carefully set your squish band clearance, that helps out with denotation as well.