I remember reading after the 125cc race that Honda blamed the weather, the day started foggy, cool and damp, the race was delayed for three hours or so, and when the race started it was very warm and dry and the carburettors were set up for the cool damp conditions making the Hondas run too rich. Whereas the Yamaha crew kept a very close eye on the conditions and altered the carbs to suit the conditions. (I think)