The problem is fuel starvation. First make sure you install a clear fuel filter between the fuel pump outlet and the carb's inlet. Check to make sure the idle mixture screw is set at least 1 turn out from slightly seated on all carbs. Check the idle screw is properly set by checking the cam line against the roller. Use proper starting procedure, i.e. prime until bulb is firm, place throttle lever in fast idle position, push in and hold the ignition sw to choke while starting.
The clear fuel filter should stay full or at least 3/4 full when engine is running. If goes empty and engine dies, then the problem is upstream of the fuel filter, i.e. fuel pump, leaky or clogged fuel hoses, clogged pick up tube, stuck check valve on the primer bulb, etc. If the engine dies but the fuel filter stays full or at least 3/4 full, the problem is downstream of the filter, i.e. carb's float settings, clogged needle port or jets, etc.
