This is getting a little like the discussion on AF447 ... lots of detail, which somewhat obscures the main problem:
All carb equipped aero engines can develop intake icing, and this will cause the engine to stop if nothing is done to remove the ice.
The desired action of a pilot is to recognise the condition, apply carb heat, and get out of the icing area if possible.
Agreed the first indication in cruise is a gradual drop in rpm. Thereafter in my experience engines react differently. If you are lucky the engine runs rough, gives some mighty bangs, and generally frightens the s***t out of you. You apply carb heat, wonder why you missed the onset of icing, and resolve to keep a better watch on the engine performance.
The other sort of engine just stops and you now have an irrecoverable situation leading to a forced landing.
It is because the latter situation continues to kill new PPLs that I am making such a meal of this thread. The regular carb heat check that I have been suggesting really works ... it gives pre warning of icing and enables the pilot to take timely action. Too many have died due carb icing, and it's time that particular danger was put to bed by proper instruction.