engine dies

Hello everyone, I just purchased a two stroke Schwinn Stingray OCC off of a gentleman this week. It's used and has been through three owners so far but the last guy didn't ride it as much as he fixed it from the previous owner. I am completely new to motorized bikes so I really don't know...

This is making my head scratch guys... My bike can go 50% throttle for more than an hour. However when I go above 80% throttle for more than 20 seconds then the engine dies off... I am 100% sure it is not supposed to do that lol. So right after it die this time I saw that the plastic...