Valentino Rossi admits he "expected a lot more" from the 2020 Yamaha MotoGP prototype rolled out for Monday's post-Czech Grand Prix test, in which he was sixth fastest.
For the first time in recent years, Yamaha brought the initial variant of the bike it will race the following season to the traditional summer Brno test - with Rossi doing the bulk of the running on the machine, which was most notably fitted with a new engine.
Rossi ended the day four tenths shy of Petronas SRT's Fabio Quartararo, who was mounted on the current M1.
Although reticent when asked to comment on the new bike's positive and negative points, Rossi conceded he expected a bigger step to have been made with the 2020 bike - despite saying he expected more to come at the two-day Misano test at the end of August.
"It was a good day, it was a good test because we worked a lot and we found some good things," he said.
"We tried also the prototype of the new bike, but sincerely we don't have a lot new [to try].
"It's a different engine and a different setting of the chassis, but it's just the first contact and it is good that we already have it.
"[The new bike has] some good things, some bad. We expected a lot more, but we know - because it's just the first time - we can also have something else in the next test in the second half of the season.
"We tried to have more grip, especially from the rear. So we tried some different settings because the rest of the bike is the same.
"We found some things better, some things worse, we fought a little bit with the wheelie. So we still have a lot of work to do."
Team-mate Maverick Vinales said after finishing a lowly 10th in Sunday's race that he would not try the new bike, as he wanted to focus on rectifying the issues that hindered him in the GP.
But he completed a handful of laps on the 2020 bike at the end of the session, going second fastest and missing top spot by just 0.012 seconds.
While pleased Yamaha is already working towards next year, Vinales said the amount of rubber on track made it unclear whether the bike had gained grip compared to the current M1.
"Well actually it's just a step, a small step," he added.
"I don't know if it's in the correct way, because we tried it when there was a lot of grip on the track.
"Normally our bike works pretty well [when it's grippy]. We have to try it when there is no grip.
"I think Misano will be very good to test it, when it's hot conditions, very slippery, and there we will know more realistic things."