Chosen Solution

After a long run, noticed a white smoke coming from the muffler and then the engine stopped. I let it cool down, checked the oil, and replaced the sparkplug. None of these helped.

Try a compression check. It sounds to me like you blew a head gasket or maybe even the head. But look here too. -OR- The case could be over filled with oil. The rings could be worn depending on the age/hours. White Smoke not good, sorry. Frank