bad mileage

[Nori]

i use to drive my super 8 50cc 4t which ones mpg's are very very good
lately im driving a xciting 500 and i was waiting for fairly mpg's but not this much
on 4.6liter of petrol i got only 48kilometres or in mpg for 29 miles a gallon
so in 100 km ~10 liter  or 28 mpg
what may be wrong with this big boy , my serviceman checked the carb and says its ok he kinda adjusted that

[guile]

Does the engine respond well? Does it rev up quickly to maximum speed or does it hold back? If so, check the diaphragm (if it has a carburetor).
BigOrange suggested this to me a year or so ago and very happy after changing the diaphragm.

[sissy mary]

I agree, change the D. (If carb model)? It is sometimes very hard to find a tear or holes in the diaphragm, but thats probable it. 

[Nori]

this problem was even last year the mechanic adjusted the carb and it came back to normal mileage , but the problem is he tried once again and said its good
but the mileage is pretty high from last year adjusment , how can i do it by myself
@guile yes it revs up pretty good it takes 60mph in no time
thanks guys for you replies i dont trust anyone to work on my both kymcos