By Peter McLaren

Masao Furusawa, Yamaha's general manager of Engineering Operations, is watching the factory's new signing Jorge Lorenzo 'very carefully' - and may ask the MotoGP rookie to change his riding style.

Lorenzo finished this week's Sepang test fastest of all, after a late qualifying tyre run, but that single-lap charge masked a 'major problem' with the front end of his YZR-M1 - something the double 250cc world champion has struggled with, to a certain degree, ever since stepping onto an 800cc prototype.

"The major problem is still the front end going into the corners; the bike is not stable and we also have a bit of vibration," stated Lorenzo, who was also forced to halt a planned race simulation because his "pace was not good enough."

On race tyres, Lorenzo lapped 0.706secs slower than team-mate Valentino Rossi - and wasn't able to beat his own previous best from the January test.

"We've tried many different things with the chassis and the suspension settings but we still have some problems going into the hard braking areas," confirmed team manager Daniele Romagnoli.

Furusawa, put in charge of turning the YZR-M1 into a world championship winning machine upon Rossi's arrival in 2004, has been able to pinpoint the main reason for Lorenzo's problems - but isn't yet willing to 'impose' a solution.

"Jorge was champion of 250 and the riding style is different. Right now Jorge sits a little bit further back on the bike," said Furusawa, speaking exclusively to Crash.net. "We modified the tank shape a little bit. The weight distribution is a little different from the standard bike.

"Now I'm watching Jorge very carefully. I would like to keep his preference for the riding position, but if it is impossible then I will ask him to change his riding style. It is just his seating position that is different compared with Valentino Rossi and Colin Edwards."

Furusawa added that it is unlikely that Lorenzo's front-end problems are down to the use of Michelin tyres, compared with Bridgestones on Rossi's bike.

"Colin has had no complaints about the front of the bike, and he is using the same tyres as Jorge. So today [Thursday] I gave Jorge Colin's bike set-up to try, but he is still struggling," Furusawa explained.

"We still have enough time before the start of the season, but maybe at the next test we will have to decide which way to go.

"For us it is easiest to give Jorge the bike and say 'please change your riding position', but I have respect for Jorge's style because he is the 250cc champion," Furusawa concluded.

Two tests now remain before the start of the 2008 MotoGP season, the first of which takes place at Jerez from February 16-18.