When you have sparks on the outside of the spark plug it can mean you have a partly fowled plug or dirt,moisture or something allowing the spark to track on the outside of the spark plug. You can try cleaning the outside of the spark plug or replace it some times the spark plug will have cracks very hard to see, or carbon tracks on the outside and it will get so bad that the engine will miss fire. I'm surprised you didn't say anything about there being a slight miss.
You might also check the gap as the spark will go the path of less resistance too much gap will also do the spark on the outside. I haven't seen a china engine do this as most have a weaker spark sounds like your engine has a good spark.
Good thing you didn't touch the spark plug when you saw that it would make for a shocking experience!
let me know how it goes good luck.
I run a gap of around 0.017 to 0.020 but I also run lights on my bikes so you could go more gap say around 0.025 to 0.028
Norman