Rotax 912 series Operator's Manual page 50

Beyond that observe following advices for operation at extremely
low temperatures:
Addendum to note 1)
Water in fuel will accumulate at the lower parts of the fuel system
and leads to freezing of fuel lines, filters or jets.
Remedy:
— Use non-contaminated fuel (filtered through suède)
— Generously sized water separators
— Fuel lines routing inclined
— Prevent condensation of humidity,
Addendum to note 2)
Carburetor icing due to humidity may occur on the venturi and on
the throttle valve due to fuel evaporation and leads to performance
loss and change in mixture. Intake air pre-heating is the only
effective remedy.
Effectivity: 912 Serie
OM initial issue
NOTE: Distinguish between two kinds of carb icing:
1) Icing due to water in fuel
2) Icing because of high air humidity
differences between aircraft and fuel.
WARNING: Fuels containing alcohol always carry a small
amount of water in solution. In case of tempera-
ture changes or increase of alcohol content,
water or a mixture of alcohol and water may settle
and could cause troubles.
AIRCRAFT ENGINES
i.e. avoid temperature
page 10 - 20
July 01/98