Sounds about right. Plenty of up and down on the throttle so accelerate then let it overun downhill or on the flat.
On the Chinese scooters i fitted new cylinders, they just rode the nuts off them included on one was a new crank and cam chain. Surprised they do not supply a cylinder kit and many sellers on ebay advertise 150cc kits for some bikes.
Those little 50cc scoots are hard to break but these 3 Grandchildren did a good job breaking parts.
The other Grandson on the Yamaha 125 had no engine problems in 5 years and mileage at 20,000. Bought for £1000 and sold 5 years later at £1000 and bought a car. I had a few rides on it but its top speed is about 58mph carrying my 16 stones. Very well built engine but cycle parts rusted easily in our salt laden air.
It used 1 rear tyre,a chain and sprocket set, 2 ignition locks and a new front mudguard following a fall, 1 complete exhaust system