In hot and humid summer weather, pilots with carburettor engines often do not think about the possibility of carburettor icing, even though it can occur in such conditions. The temperature in the carburettor can drop significantly due to the Venturi effect and fuel evaporation, so ice can form if there is enough water vapour in the air. This can impair engine performance by restricting the mixture supply to the cylinders. Icing is most likely to occur at temperatures below 20 degrees and high humidity, but is possible even at temperatures as low as 38 degrees and only 50 per cent humidity.
Only aircraft engines with float carburettors are affected; injection engines are not affected. To counteract carburettor icing, the pilot can activate the carburettor preheater, which heats the intake air and thus prevents ice formation. Some aircraft models are more susceptible to carburettor icing than others, depending on the position of the carburettor in relation to the engine and the respective flight phase.
If there is an unexplained drop in performance, the pilot should consider carburettor icing as the cause and can check this by activating the carburettor preheating. It is important to keep an eye on the intake air temperature and follow the instructions in the flight manual to ensure that the pre-heater is working properly and to take effective action against icing.
The video explains the topic very well!
Source references:
YouTube video on carburettor icing
