Please bear the following in mind....I AM NOT AN AVIATOR.
ISTR Rotax engines having a "needle and slide" (Bing?) type carburettor.
Wear in the slide/body can cause air -leaks and allow the needle to fret on the jet...needle -flutter causes uneven mixture, which would probably mean a wider throttle-opening for the same power-output.....(if you've got good CHT monitoring and lean-out, , that eliminates that suggestion.
The english SU carb. attempted to meet emissions legislation by having a main-jet mounted on a bimetal strip, (fuel-temp compensation)combined with a wax-capsule at the jet-base ( ambient air compensation) and a needle spring- biased against the jet (eliminating flutter) Of course, it worked fine for a short while , until the needle sawed the jet-orifice oval and a corresponding wear-mark down it's length.....fuel consumption increased dramatically.
the giveaway, was an extremely rich tickover, with virtually normal full throttle AND LOAD operation. or, if you weakened the idle mix to a satisfactory state, thething would starve and fluff or die as you opened the throttle. new needle and jet was a cure.....similar situation with AMAL motorbike carbs.
HTH.