I have a 110cc with a pz20 carb
it runs great after it gets warmed up. If I run it all out it moves
I've done the tuning of the carb best I can from all the videos.
but my son with stall it often and I assume its because it keeps blipping the throttle.
When I ride it I ease off the gas more like a foot or hand but with the thumb throttle you can easily just let go.
it will tend to stall if you just let go of the throttle.
I dont feel the idle is too low in fact I would like it to be lower but....

 

Fit a new plug. Even if you have done it before, clean the carb out properly. I always go for removing and blowing out both main and idle jets, and the holes they came from. Stuttering or even cutting out when you open the throttle quickly is common if the mixture is a bit lean, but there should be no stalling at idle no matter how fast you take your finger off. If cleaning doesn't help, check the float level and, if that is OK, you may have to alter the idle mixture screw or even fit a different idle jet.