The inventor describes a method of facilitating the starting of internal combustion engines having a scavenging pump, consisting in raising the temperature of the scavenging air by causing the scavenging pump to work during the pressure stroke, against a greater resistance than otherwise; the air thus heated being delivered to a passage connecting the said pump with the working cylinder of the engine, the pump being caused to suck back part of the air delivered to the said passage, and the air thus heated to a higher temperature being supplied to the said cylinder.