It may be that the diaphragm is not working .. try buying a gasket and diaphragm kit, clean all the carburet and uncover it, assemble it well and carbureted at first with 1 turn to the H screw and 1 and 1/2 to the L. Dsp lo regulations in progress. If it is not solved try to check the crankshaft seals, it may be sucking air out there ... if you do not try when it stops, open the carburetor and see if the tanks have naphtha, if it is because it is sucking air somewhere, but, it is because the diaphragm does not operate with the vacuum of the engine and does not open the needle of the naphtha passage .. greetings!