So that's detonation for sure. Less likely to be timing or too hot a spark plug which tend to kill the centre. I'd say too lean jetting or airleak. The longer time under full load may have exposed a long standing issue.
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'07 EC300 GG
'14 TXT250 GG
'? 496 CPI Cheetah RZ/RGV hybrid
'22 765 Street Triple RS
'21 XTrainer
'69 Stinger T125 Suzuki
'23 TRS 250RR (it's a Trials thing)
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