Temperature, humidity, altitude, fuel load, mixture, ethanol concentration and wind and any other element I maybe forget have an effect, especially on a motorcycle with a narrow powerband like the Honda NSR150 SP. Up a steep hill the extra weight of a full tank of petrol can alter a motorcycle's power-to-weight ratio enough to be noticed. Wind is a factor at higher speeds and can easily add or knock off 30 km/h from a motorcycle's top speed.
Temperature, humidity and other elements affect a motorcycle's carburetor fueling. This is particularly significant on highly-tuned two-strokes. Get out on a cool, dewy morning and it should fly compared to a hot and more dry afternoon...