Rotax four stroke aircraft engines have proven themselves as reliable pieces of machinery. They can be bought as experimental (UL), sport (S) or certified (A and F) engine and there are four main models (fuel injected too: i models) to date. The original engine is the 80 hp 912, from which the 100 hp 912S was developed and Rotax also has a 115 hp turbocharged 914 engine. In 2015 Rotax announced the fuel injected 141 hp turbocharged 915iS.
Due to overtorquing, vibration, fuel containing more than 5% alcohol, non approved intake airbox, or other engine imbalances the carburetor flanges are probe to cracks on the inside.
The flanges must be checked every 50 hours time in service for crack, distorsions, damage, wear according to this service bulletin and if needed replaced.
SB-912-030-914-019-R1, Carburetor Flanges
Excerpt from the document:
Introduction of an optimized carburetor flange with improved strength properties and spacer for the clamp. One or more of the following could result in increased stress and consequently in damage of the carburetor flange assembly:
Over-torque of the flange clamb, unapproved and untested changes of installation, as for instance carburetor installation with intake manifolds pointing outwards, use of an airbox assembly and airfilter not approved or distributed by ROTAX
Improper carburetor synchronization: unsuitable idle speed (too low), unsuitable engine suspension / non-neutralized vibrations, propeller balance out of tolerance.
To continue reading see the pdf below: