I picked up a QT50 as a project and the previous owner had drilled two 3/8 holes in the exhaust. I found a way to plug the holes and continued to work on getting the moped running. The carb was missing pieces, so I ordered a new one (clone).
I was able to get it running, but I believe that it's running very rich. To get it started, I have to hold the throttle 1/4 open. The Idle adjustment screw is bottomed out and the pilot screw is out 3-4 turns. There is no air filter on it either. I can get it started but it quickly gets very smoky. The carb is new so it should be clean and stock sized.
Additionally, this morning , I un-plugged the 2 holes in the exhaust and the moped ran much better. Still rich, but a lot less smokey. I was going to try to adjust the float, but I'm not sure if that will help.
On a side note, I can unscrew the pilot jet, but I can't get it out of the hole. Not sure if anyone has any tips on that too.