A carburetor for feeding internal combustion engines, comprising an outer shell (2), which defines internally at least one air and fuel mixing duct (3); the duct (3) is interposed between at least one opening (4a, 4b) for the inflow of air and an outlet (5), which can be connected to a combustion chamber of an internal combustion engine; moreover, the duct (3) is affected by at least one nozzle, for introducing the fuel to be mixed with the air, prior to sending to the combustion chamber of the internal combustion engine; the carburetor comprises at least one trimming element (7), which is constituted substantially by a stem (8) that can move selectively between at least one first configuration for free passage of the air through the at least one opening (4a, 4b), and at least one adjustment configuration, in which the stem (8) is arranged so as to at least partially obstruct the at least one opening (4a, 4b), with consequent reduction of the overall passage section available for the inflow of the air.