Valentino Rossi began his 24th year of motorcycle grand prix by setting the sixth fastest lap time during the opening day of official MotoGP testing at Sepang.

The Italian had finished the season-ending Valencia and Jerez tests somewhat underwhelmed by the two prototype engine options presented by Yamaha for the 2019 campaign.

Although Yamaha management had suggested there would be some further engine parts to decide upon this week, Rossi said he has just one type of engine in Malaysia.

"I have just one engine in this test, because the two configurations that we had, now Yamaha bring just one," he said in the paddock on Wednesday evening.

"I'm happy with the choice, yes. Between the two are not a lot of difference. But the engine is not so bad."

However, Yamaha has made a further evolution to the engine favoured by both Rossi and Vinales late last year, leaving the soon-to-be 40-year-old satisfied.

"In Valencia and Jerez we had really, really small things. Not a lot," the Italian said. "Here we have some bigger things, more important.

"We work a lot on the engine brake, especially because Maverick always pushes from this point of view and is right. We have something better and also some different things compared to Jerez."

The #46 confirmed he expects this engine to be the version he uses when the racing season begins: "Sincerely, I have just one engine and it is more-or-less already decided [it will be raced]."

Rossi added: "I'm happy that - especially when we speak together with the engineers and also with Maverick - we are all working in the same way.

"So we are agreed about the weak point of the bike… From this, to fix, we have to work!"

Looking to rebound from his first ever winless season on a Yamaha, Rossi's priority is to improve the performance of the M1 with used tyres, which also means making the tyre last longer.

"The first day is quite positive because I have good feeling with the bike from the beginning and it also looks like also with the used tyre, which is our weak point, we are not so bad," said Rossi, who was 0.43s from Honda's Marc Marquez but only 0.12s from Vinales.

"We tried something today that improved a little bit the performance. It's s all together engine, electronics and also chassis side of the bike. We try to work with the used tyres and if you look at the lap times, with the other guys, we are not so bad.

"For me, we start in a good way, but we need more."

Testing continues at Sepang on Thursday and Friday.