Yeah you just need to clean the carburetor.
Your main jet is clogged, 5 to 1 odds.
You don't need to buy anything besides a can of carb cleaner.
If its the first time you are doing it have a buddy there to make sure you don't leave anything out.
Luckily its a pretty easy carburetor to clean.
Just pull it off the bike. You can even leave the top on if you want. pull the bowl off, clean it out maybe with carb cleaner and a toothbrush, then unscrew the main jet.
You are going to need like a spun out brake cable or some kind of tiny wire to poke through the main jet.
There are plenty of videos on youtube.
Not sure if there are any QT50 specific videos but any Jog or Zuma carb is going to be almost the same thing.