Maverick Vinales said a late-session change on Day 2 of the Buriram MotoGP test has improved his Yamaha, and led him to discover a problem with the bike.
One of Yamaha's main issues throughout the 2017 MotoGP season was rear tyre life and, as a result, the team attempted to fix those issues with the 2018 machinery.
However, Vinales says the bike was made too "smooth", and a change in the electronics during the second day of the Buriram test has improved the performance.
"I think we made the bike too smooth, that is the problem," said Vinales, who ended the day in fourth.
"We were looking for so much smoothness and we barely stressed the tyres.
"We tend to have a smooth power delivery and I'm probably better off with a bit more aggressive [style].
"Until the last 30 minutes of the afternoon, honestly, we've been doing so many changes on the bike, trying to find the way.
"We changed electronics, we tried to make more easy bike, especially on the beginning of acceleration, and it seems to improve."
Rossi continues to struggle
On the other side of the Yamaha garage, Valentino Rossi, who ended the day in 14th, says he "didn't find the good solution".
The Italian was also working on electronics, trying to improve acceleration.
"It was a difficult day. We start this morning in quite a good way, I did some good rhythm, I was faster compared to yesterday, not so bad.
"But after we have a long list to do, a lot of work, we work a lot with the setting for try to improve.
"We work a lot for the electronics to try to improve the acceleration. But sincerely we don’t find the good solution.
"Unfortunately during the day we are not able to improve, sincerely I don’t feel very comfortable. We need to do something else tomorrow."
Additional reporting by Oriol Puigdemont