Originally Posted by jrzyguy
needed to hold throttle open to start, would shut off at idle
These two indicate a clogged pilot jet. It wouldn't be the first time that someone cleaned a carb and didn't actually get it clean. Pull the pilot jet and inspect all the holes. Clean them with a very fine strand of wire and compressed air. A droplet of water can clog it. Clean every passage of the carb with a pipe cleaner and air.
It doesn't sound electric at this point.
I wouldn't place too much on reading the old plug. It tells the story of many thousands of miles. The new plug says a lot more about how the bike is running today.
Good luck and don't give up. Take it to another mechanic if you need to. Someone else in that town can fix motors. Even a lawn mower guy knows how to deal with fuel and spark.