Surging not under a load and dieing with a load sounds like it is starving for fuel or air. Put new air filter and sock on it, make sure the airway to carb isn't plugged. Then go to the float in the carb and check needle valve(s). Also, since it has been running lean or rich, get a new sparkplug in it. It isn't a shotgun approach, just when you do solve the problem, the other parts of the system have been working to compensate.