Hello , ride a 4 timer scooter Benzhou !! Kilometers are almost 19000 km on it !! Carburettor cleaned ( ultrasonic ) ,new belt ,new clutch and new exhaust made !! my scooter drove at first between 55-60 ,now it runs only 45 ,and mountain on 40 ,and I have the feeling that it is getting less and less !! Carburettor was also set ,empty speed , lies between 1500-1800 Umin !! In addition I must say that it comes short still black exhaust gases from the exhaust (if you hand the before it stops , she becomes black ) !! He also takes bad gas !! He also brakes while driving !! Please for help !!