Valentino Rossi welcomed the latest modifications to Yamaha's 2020 MotoGP prototype, delivered to The Doctor and team-mate Maverick Vinales for this week's Valencia test, but warned they don't go far enough.

The new bike featured a slightly revised chassis and, more importantly, third evolution of Yamaha's 2020 engine, after earlier versions were tried by the race team at the Brno and then Misano tests.

"The new engine is smoother than last year‘s, and we also increased the top speed to a certain extent," said Yamaha team director Massimo Meregalli.

The words 'certain extent' confirm that the new engine is still lagging behind the likes of Ducati and Honda, with Rossi hoping the Yamaha engineers can squeeze more from the powerplant in time for next year's Sepang test.

"We try to be faster in the straight and the bike is a bit better but the way is still long," said Rossi, who rode for 68 Wednesday laps and was one of the last riders to finish testing.

"For me, we move in a good direction, but still the [top speed] gap is big.

"This is the third [version] and already the engine is improved, but we hope that Yamaha don’t give up, because we need another step in this way before Malaysia.

"Now in MotoGP it's a big package, but the engine is where we need to improve."

Yamaha riders filled the top three places on the timesheet during both days of testing courtesy of Vinales plus Petronas riders Fabio Quartararo and Franco Morbidelli.

Rossi has long abandoned chasing fast laps in testing, and finished with the ninth quickest time (+0.932s), but felt his pace had improved 'a lot'.

"The engine they try to make something more easy to ride to save the tyre and it's a bit better. Not so bad. Also for me the new [Michelin 2020] tyres are better. More constant. So this is a positive.

"Also the chassis is a bit different, something better, something worse."

Pressed on what exactly he meant by that, Rossi replied: "In general we try to have more grip. But when you try to create more grip, you have some other problems. So the bike is a bit different to ride.

"We work just yesterday because today mainly we work with the old bike because we have a small problem with the new bike. So the way is long, but the feeling is positive. Now we have to work.

"And from the other side I have some difference in the team, chief mechanic, so it's very important to understand and try to work together.

"But both things [bike and crew chief] are positive and at the end I am P9 but we improve a lot the pace with used tyres, that is very important."

Rossi is now eager to see how the new bike performs during the final test of the year at Jerez next week.

"This is very important," he said. "You understand more at Jerez because it's very similar to a lot of other tracks, whereas Valencia is very small and different. We will have the same stuff so we will try the prototype again."

Quartararo and Vinales, who remained on the 2019 bike at Valencia, also hope to try the new engine at Jerez.