Valentino Rossi has been forced to test his 2005 Yamaha bike in an attempt to revive his poor early season form.
Rossi suffered bike problems in the build-up to the new season
The World MotoGP champion crashed on lap one at the season's opener in Jerez last week but recovered to finish 14th.
The teams have stayed in Spain for further testing and Yamaha boss Davide Brivio said: "We've let Valentino ride the 2005 bike for a few laps.
"We wanted to compare its performance. It was interesting to see that a few things about the 2005 bike are better."
Sunday's outing was the first time Rossi had failed to win the opening race in six years and followed a host of problems in pre-season testing.
But Brivio insisted that the team collected some vital clues from re-running last season's machine.
"It was a very useful and interesting day for us and we were able to collect a lot of important information which we believe will help us," he said.
Repsol Honda's Nicky Hayden topped the timesheets in the test day in Spain with Spaniard Sete Gibernau (Ducati) second.
Rossi's Italian rival Capirossi (Ducati), winner of Sunday's race, was third quickest.
The next round is the Qatar Grand Prix on 6-8 April where Rossi will attempt to get his bid for a sixth consecutive world title at motorcycling's top level back on track.