A new variable venturi carburetor has been developed, in order to achieve high metering accuracy, fuel economy, higher power and good driveability of the vehicle. This carburetor is a down-draft-type, and has better characteristics compared with the fixed venturi carburetor, such as better fuel atomization, lower cycle-to-cycle variation of combustion in lean mixture, faster response, and higher power. For this carburetor, a new type venturi and a new cold enrichment system has been developed. This venturi type has an exponential-profile with a nearly constant increasing rate of venturi opening area to the suction piston stroke. The new cold enrichment system controls the airfuel ratio in all conditions by changing air bleed quantities using the thermo-wax. With this system, cold drive-ability is improved greatly.