Tweaked '21 or tweaked '28 makes near zero difference, what will make a difference is safe jetting in Japan for any weather compared to on the edge jetting in 97°f, you might well find it's 4 or 5 sizes too rich.
As Dave Ett knows you can have a good engine jetted badly and make a damn sight less than 49bhp. What was it Dave for your first race?
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Please do not PM me technical questions, if you can't find it on the Forum start a thread