The Rotax carbs do have some altitude compensation but it is a primitive mechanical system. I sometimes wonder how rich or lean the engine really is.... and then I just go back to flying.
from my undersanding,( i could be wrong, more data on this would be good) the Rotax Bing carbys are good to maintain Mixture to about 9000 ft, ISA conditions, but the risks of damage from running high CHT,s from high internal pressures are reduced with higher RPM, and water cooled heads. Higher RPM actually lowers the internal cylinder pressures when running at the worst spot of about 50 deg ROP.
As for helping get correct air fuel ratio and vapourisation, the 912 ULS operating manual suggest the best carby air temp be kept at 21 deg C. (going from memory)