Your carb is dirty inside.
Anytime a bike runs with the choke on ... but won't run with the choke off.. thats what it is.
I will repost my "Fix your Ped" guide above in a second.. Read in there about how to clean the carb.
The problem with cleaning a PA50 carb is getting the carb out(big pain)... the best way is to suspend the frame from an overhead rafter and hoist the stand just a little off the ground... then remove the bottom R shock mount bolts... and the large "through frame" bolt under the footboards... then the throttle cable at the carb... then hoist the frame a little more... and swing it out of the way.
....There is the carb...... (I find it best to leave the reed block attached (so just take out the 4 screws on the motor)