I can´t find any good info on that anywhere……….
I happen to have an old Europa brochure here with engine info on both the 912ULS and 914UL (but not the 912UL unfortunately)
Between the 912ULS and 914UL the performance figures are remarkable similar with one main exception: the "take off" curve from the 914 is higher in every respect: power, torque and fuel consumption. Obviously that's the time when the turbo is most active.
But other than that the fuel consumption for a given HP seems almost identical between the two. The graphs in the brochure aren't all that good but it looks like the 914UL is even using slightly less fuel (<5% difference) to produce a given power than the 912ULS.
I was looking at the Rotax site and it seems that you can get the original datasheets directly from them. Doesn't that help?
Aircraft - DOCUMENTATION