Yamaha say that the most likely cause for the Rossi and Lorenzo engine failures was the undulation on the main straight of the Italian circuit. At that point, the rear tyre – spinning at around 380 km/h in the air – loses grip, leading to an increase in revs per minute for the engine. Rossi’s engine failed after only 500km. Source:
That, combined with this year’s electronics, which are less sophisticated and precise, probably had an influence in the ignition cut-off…Valentino was running behind Jorge all the time, and that probably meant he had no clean air to cool down the engine.. Running in his slipstream meant Rossi’s bike reached speeds it had not managed during the weekend.