Methods of operating a diaphragm type carburetor to facilitate the atomization of fuel in the diaphragm-type carburetor are disclosed. Particularly, methods of operating a diaphragm-type carburetor having a check valve installed in a fuel passage leading from a constant-fuel chamber to a main nozzle, and an air bleed passage connected at a position on the downstream side of the check valve are disclosed. Moreover, techniques for operating a diaphragm-type carburetor having a main nozzle including nozzle openings facing downstream with respect to the engine intake air flow are also disclosed, wherein the nozzle openings are located in a tubular member cutting across a central axial line of the venturi so that the tubular member bridges the neck of the venturi.