Taking the thread (only slightly) off topic... the Rotax 914 also doesn't have a mixture control. The 914 is (AIUI) basically the same engine as the 912, but turbo-charged (with the turbo-charger being pretty much totally automatically controlled).
I had always assumed that the reason for the absense of a mixture control on the 914 was simply because the turbo-charger prevents the manifold pressure from dropping with altutide, and therefore leaning is not required. I'm slightly surprised to hear that the 912 doesn't have a mixture control either, since that dis-proves my theory.
Sorry for the thread diversion!
FFF
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