To successfully maintain an engine running condition by avoiding the temperature rising in a carburetor.

A combustion chamber 15a is formed in a cylinder head 15 of an engine 25 mounted on a vehicle. An suction port 15b and an exhaust port 15c communicating with the combustion chamber 15a are formed in the cylinder head 15. A carburetor 27 for feeding air-fuel mixture into the combustion chamber 15a is arranged at a vehicle rear side of the engine 25. A suction pipe 35 for guiding air-fuel mixture is provided between an output port 28b of the carburetor 27 and an suction port 15b of the engine 25, and a heat shield 36 is provided in the circumference of the suction pipe 35. Because the traveling wind heated after cooling the engine 25 is guided along the heat shield 36 to the outside the suction pipe 35 in the radial direction, temperature rising in the carburetor 27 can be avoided without being directly sprayed into the carburetor 27, and a vapor lock accompanying fuel bubbling can be avoided.