Well, at my second ROTAX practice session, my ribs held up just fine . . . but only because my clutch expired after only ten minutes of running. Turns out the nut that holds the chain sproket to the clutch housing had come off, which of course leaves the kart with no drive whatsoever. Wasn't hard to fix, except I needed to buy an impact wrench to get the clutch opened up in the first place.
I guess the guy who owned the kart before me didn't bother to use lock-tite or some similar goop to help hold the nut in question in place.
Hopefully, I'll learn how to avoid these little mechanical gremlins relatively quickly. 4 hours of towing/kart preparation for ten minutes of seat time is not exactly my idea of a good return on investment, timewise!!