Rossi: new engine marginal on fuel

The Italian is keen to use the engine in tomorrow's San Marino Grand Prix, but he admitted that at present it is doubtful whether the engine is capable of making the mandatory 21 litre fuel allowance last until the end of the 28-lap race.

"It's quite difficult with the fuel consumption to make the whole race - it depends on the temperature and on a lot of factors," Rossi said.

He said Yamaha already had fuel mileage issues with their standard power unit, and that the problem was exacerbated by the upgraded engine.

"It's a little bit worse. Already we are at the limit with the normal one, so we have to make our calculations," said Rossi.

"We were at the limit with the fuel at other racetracks this year, so we'll make the calculation and then decide.

"From my point of view, I want to use the new engine. The engineers are trying to understand how much it is risky, but I think we'll try."

Rossi had been unsure about the engine after running it for the first time in testing at Brno last month, but he is now convinced of its merits.

"I like the new engine, it works well," he said.

"The difference is not a lot, but it worked like we expected and we're 2km/h faster, more or less. It's difficult to understand here because the straight is quite short.

"But we have a small improvement, especially in the high gears."

Yamaha have struggled to match main rivals Ducati for straightline speed for much of the season, with the Ducati power advantage proving crucial to several of Casey Stoner's early-season wins.