While running a 520 to operate a King Kutter 6' tiller it starts out running fine. After several passes it starts to run terribly and will not run at all w/o the choke applied. Even at full choke it runs badly, barely running at all limping back to the shed. After letting it cool a while I started tilling again, running fine, and the same thing happens again. I did notice the temp was nearly 200 degrees. Is the tiller too much for the 520 or is the carb in need of rebuild? It has new cooling fluids, engine oil, points, cond, rotor, cap, plugs 15 hours ago. Your suggestions for a solution or cause are needed.