The fuel-air mixture for the 2-stroke / 4-stroke engine of a scooter or moped is produced in the carburetor. The principle is relatively simple: air is sucked in on the one side of the carb, the air is compressed and diffused in the carburetor and mixed with the fuel supplied by the main jet. The mixture then enters the cylinder via the intake system. The best known manufacturer of carburetors is Dell'Orto with a huge catalogue of carburetors in all sizes and different versions with or without oil/vacuum connection, for cable or e-choke and with round or flat slide. PWK, PHBL, PHVN, VHST, PHBG, PHVA are some of the most popular Dell'Orto models. Brands like Stage6, Malossi, Motoforce and Malossi also build high quality carburetors, all based on the same design principle. In addition there are carburetors from Keihin, Mikuni and Gurtner. You should always make sure that the performance of your carburetor matches that of the cylinder, i.e. when upgrading to a more powerful cylinder, it is recommended to use a larger carburetor.