Abstract: A fuel inlet system (12) for an internal combustion engine (10) comprises a heat exchanger (22), heated by engine exhaust gases, to preheat air being supplied to a carburetor (14). The air is introduced into the carburetor (14) at a temperature of between about 375.degree. to 400.degree. F. The carburetor (14) has an annular heating chamber (122) in which the heated air is circulated. A fuel inlet conduit (63) is in thermal contact with the heated air in the heating chamber (122) to preheat the fuel. The air and fuel is mixed in two stages, the first being during travel along a conduit (144) and the second in a mixing chamber (170) in the carburetor (14). The carburetor (14) includes a valve (148) for restricting the amount of air flowing to the mixing chamber (170). The fuel inlet system (12) further comprises means (20) for adding water to the air/fuel mixture.