Mixture & Carb Heat

The 914 does not require carb heat because the turbo heats the air enough that carb icing is not an issue.

More food for thought:

The variable throat Bing 64 carb helps stave off carb ice, but it can and does still happen. The folks in the UK have more days where temp and humidity are just right for this. The owners with an engine in a cowling and their air filters are attached right to the carb and use under the cowl hot air vs outside the cowl cooler air run in carb heat mode all the time and they run a bit richer just like when you actually add carb heat.

Mixture control is automatic via the carb pistons.

My 912ULS does not have any cowling, but I have a system that circulates warm coolant in a collar around the engine end of the carb, intended to warm things enough to prevent icing (see left of photo).  Obviously such a system is not possible in an engine without liquid coolant, where the air itself has to be preheated to prevent carb ice, causing the side effect of making the intake air less dense.