How sad that after all these years carb heat is still a problem. Lycosaurus engines have been around for two centuries! Surely by now the PPL training schools should have perfected carb heat instruction so as to make engine induction icing a non event. Faffing around with carb heat, using up valuable thinking space when other things need your attention is potentially disastrous.
So all air cooled carburetted aero engines WILL ice up sometime, some more than others.
A pilot needs to avoid ice build-up before take-off by selecting carb heat on after engine start, and off just before applying take-off power.
On again for the downwind check, and off when applying take-off power for a go around.
In flight the standard engine ice check should be performed every ten minutes on your FREDA check. (E = engine: check Ts & Ps & Ice)
Hands up those who have forgotten the standard in-flight engine ice check?
1. Set cruise power, and ensure engine rpm is stable.
2. Apply carb heat and observe engine rpm: If there is an immediate drop in rpm and no other indications, select cold and look for an immediate return to cruise rpm. The engine is free of ice ... continue for another ten minutes.
3. Apply carb heat and observe engine rpm: If there is no drop, or a rise in rpm, with or without other indications, you have an iced engine. Leave carb heat on until rpm stabilises and condition 2. above returns.
This check should become habit ... you should be able to do it automatically ... it should not use up valuable thinking space which you need for non routine decisions & emergencies.
One day all engines will be diesel or fuel injected, but meanwhile we still need to learn engine intake ice management by rote ... otherwise new young PPLs will continue to die needlessly in completely avoidable icing incidents.