If you don't know what jet your running you are lucky it ran at all before.
Tackle the jetting problem before you seize the thing. Hell maybe you already did and that's your problem now.
Mopeds are two strokes, meaning fuel and and oil, as in lubrication are mixed. Too lean and your engine isn't recieveing lubrication. And you can seize.
Pull the cylinder and check the bore Piston and rings before continuing troubleshooting.