Carb ice

The chances of getting carb ice on the 914 are very slim as you get warm air pumped into the carbs by the turbo and have an airbox installed. The carbs also sit on top of the engine, above the 3,4 exhaust manifolds where the hot air rises. The engine still draws in warm air from the turbo regardless of the RPM. 

If you had a 912ULS or a 912UL without an airbox, then you would consider a carb ice prevention system such as the Rotax airbox with heat muff baffles or a cozyCarb heater - https://www.cozycarb.com/rotax-912-912s or an electric Carb heater kit https://www.rotacrepair.ca/portfolio/rotax-582-overhaul/

For your application, if you wish to install a Carb ice prevention system, it would be easier to go with the electric carb heater from RotaxRepair. 

I have Vans Aircraft RV-12 with Rotax 912ULS.  No carb heat is required.  No mixture either, for that matter.  Makes engine behave like a mechanical FADEC having single engine control (throttle).  The carbs get heated air from tightly cowled engine.  The carbs reside directly behind the cylinder heads (unlike Cont & Lyc) and stay warm from the induced air flow.

The assumption that the turbo is ever inactive is false unless it’s broken. Even when operating at lower rpm with less boost the air is heated by the turbo.

James Stricker wrote:

I have Vans Aircraft RV-12 with Rotax 912ULS.  No carb heat is required.  No mixture either, for that matter.  Makes engine behave like a mechanical FADEC having single engine control (throttle).  The carbs get heated air from tightly cowled engine.  The carbs reside directly behind the cylinder heads (unlike Cont & Lyc) and stay warm from the induced air flow.

I wouldn't be so sure about that. My 912 is tightly cowled in a motorglider and I've gotten carb ice before, albeit at low power settings. Having the Rotax airbox and a heat muff around the exhaust, it wasn't a problem. The factory AFM states to use carb heat at temperatures below 10 degrees C.

If a single throttle control is a FADEC, it's an extremely crude one. The ULS runs rich pretty much all the time and, though somewhat compensated, gets richer with altitude. The spec'd specific fuel consumption of 0.48 lb/hp/hr is quite lousy; a Lycoming, casually leaned, will do 0.42 any day of the week. The 912 iS of course is much better in this regard.

I flew my last Rotax 912ULS for 10-12 years with no carburettor heat. I was curious as to the air temperature going into the carb's - used one of those fridge digital temperature gauges with a thermocouple on a long lead. Turned out carb inlet air was around 10C above ambient.

Seems to me the two factors that will determine if you need carb heat are; the climate you fly in and the design of your engine cowling.