70km/ltr , i am quite sure your carb is set to lean, its not good, if you tried lot for getting top speed on this setting i worry, there will be chance of seizure, first of all get richer the mixture, and when you will have done the correct air/fuel ratio you will automatically feel the difference, its so simple more power with less fuel is impossible, one can easilly check the correct mixture setting by viewing the plug condition, it should be brownish or light brownish, black or light grey are not good, thanks