Maverick Vinales says the Thailand MotoGP test has been "by long the worst" for him since he joined Yamaha, as he struggled on the final day following a promising Saturday.
The Spaniard claimed that he found the solution for the Yamaha YZR-M1's traction problems at the end of day two at Buriram, saying the bike was too smooth.
However, he slumped from fourth to 12th in the timesheets on Sunday and summarised the Thailand test as his poorest ever since he joined Yamaha for the start of 2017.
"For me, by long the worst [test]. Even in Malaysia, it was the worst one that I've been in with Yamaha and this one was even worse," said Vinales.
"Today we struggle much more than yesterday; I think we had the solution, but finally not. We miss a little bit in all areas.
"Maybe it was new tyre and I was excited by incredible laps but finally this morning, when I get up on the bike, was completely the same problem as always."
Vinales revealed that he returned to using the 2016 chassis, and tried experimenting with set-ups that "we were never going to try".
"I'm using that [2016-spec] chassis and there is no solution, I don't know," he explained. "We have different engine, different electronics so I don't know, honestly I don't know.
"Maybe better ask Yamaha. I try many things in these two tests and I don't know now.
"For sure we will continue but I don't think the problem is in the garage, it is something more because we try everything on the bike, set-ups that last year we were never going to try because impossible to work.
"Honestly, Yamaha has to realise that we have a problem and they have to put the work."
The MotoGP field has one more test in Qatar before the season opener at the very same venue, but Vinales reckons it's too early for Yamaha to come up with new solutions.
"Maybe it is too close, the test," he said. "It is difficult because maybe we realise now we have a problem and it is just one month to the race."
Additional reporting by Oriol Puigdemont