After his first day with MotoGP's new compulsory ECU, Valentino Rossi stated it felt like "a jump in the past: 2008-2009" compared with the bespoke Yamaha system.

But significant progress was made during the second day of last month's Valencia test - the final MotoGP action of the year for Rossi and team-mate Jorge Lorenzo, the newly crowned triple champion.

Lorenzo's team manager Wilco Zeelenberg told Crash.net that Yamaha had "caught up about three or four years" relative to Rossi's '2008-2009' day one assessment, but with plenty still do to.

"It's true that we still need to work on that a lot and of course these bikes - from Honda and Yamaha - were very finely tuned in this area: Wheelie control, traction control, engine braking, all these matters," Zeelenberg said.

"Now they've changed suddenly to [an ECU] system that has never been tested before. So it was not strange that they felt lost on the first day. 'Whoa, whoa, what's happened?' But as soon as they can read the data, they can see what is going wrong and now it is a question of adjusting everything."

Repsol Honda's Marc Marquez had complained that the new system was cutting the engine too aggressively and preventing any smooth slides.

"I think that's also the case for us. I can't give a specific answer because I have not been on the bike but from what I hear from Jorge it [the ECU] is controlling a lot and not in the right way," Zeelenberg said.

Lorenzo finished the Valencia test as the top Yamaha in fifth, with Rossi seventh.

While closest rival Honda then used three days at Jerez to gather further data for the ECU and Michelin tyres, Yamaha opted to save all of its private test days until 2016 meaning Lorenzo and Rossi will next be on track at Sepang in February.