48 cc QMB139 issue with rear wheel

[kram6319]

I had my Gator 50 scooter serviced yesterday it is a Chinese scooter a QMB139. I noticed often when I accelerate from a stop it seems to "catch" or feels like all the sudden it "goes"
It runs well and the mechanic also noticed the issue and while it was on the stand ( not the kickstand) he noticed the rear wheel didn't start moving until he gave it a good bit of throttle. He checked the brakes to be sure they were not sticking and he seemed a bit stumped. He said it's not "really horrible" but the rear wheel should free spin at a lower rpm than it does. It runs well and I don't notice that "catch feeling" all the time but it is there. My scooter has 800 miles on it and has had the rear end fluid changed and that was also checked.
Any idea what this could be??