sounds like reedflutter.........Im also gonna say the sparkplugs gonna be black..............I'll take picture tommorow(Danish time)!
But i found Out of, When it die and the motor stops, it Can't start, i have to wait 1 min. And then i Can start it and drive i bit again, also with semi High RPM?
The insulator needs to be richer brown like caramel and the outter ring needs to be less black ...........Here some pics of my sparkplug...
Which screw?Plug looks like its OK to me, the tip is golden brown the way it should. The reeds could be fluttering still.. If it were an air leak or lean condition the plug would be grey and dry. Your idle adjustment might be wrong, probably too high. try slowing the idle down a quarter turn at a time, ride it and see if it gets any better. the idle adjustment is the brass spring loaded screw on the side of the carb.