To provide a small-size engine having a forced air cooling system, wherein the amount of protrusion of the air intake system outwardly from the engine body can be minimized and the limitation on the space required for installation of the engine to the various work units can be alleviated, the engine includes a cooling fan (9) mounted on one end of a crankshaft (4) and has a longitudinal axis (S) of a cylinder block (5) inclined relative to a horizontal direction and also to a vertical direction. A fan housing (17) for guiding a cooling air (W) from the cooling fan (9) towards a cylinder block (5) and a cylinder head (6) is formed with a cutout (22) through which a float chamber (23) of a carburetor (15) is positioned inside the fan housing (17).