Common opinion for Chinese 70ccs - avg 55km/liter, mine used to give me around 65km/liter consistently for almost 6 years.
Now I own Sprinter, a common opinion - avg 50 - 55km/liter, mine gives me 68km/lit consistently for last 14 months (since I own).
It all depends not only on the good condition of your bike but also the way you ride and the road conditions. Bad road conditions, 1st - 2nd gears, high RPMs, hard pick up are catalysts for low fuel mileage.