2stroke ownership rule number one, lesson one, try another plug.
Lesson 2 repeat lesson one with another plug.
Not kidding, lots of 2 stroke ills come from bad plugs and in the case of yammy powervalve motors the battery as well, as the signals can get messy and make it do some daft stuff.
Then lesson 3 clean the carb internally.
There you go 2 stroke ills in a jiffy