Factory Yamaha riders Jorge Lorenzo and Ben Spies struggled to notice an improvement with a new-spec M1 engine, debuted at Monday's Catalunya MotoGP test.

"We tried a new engine spec today that in theory is more powerful. Until now we didn't find any big improvement, some little advantages and some little disadvantages," said race winner and world championship leader Lorenzo.

"In Aragon we will try some modifications to the electronics to see if we can gain something."

Team-mate Spies, who fell while battling for the lead of the race, gave a similar verdict although he acknowledged that riders always have high expectations of such developments.

"We tried a different engine spec and played around with the electronics. The engine spec was a little improvement but you know riders, we always want at least 10km faster on the straights!" said the Texan.

Tech 3 Yamaha riders Andrea Dovizioso and Cal Crutchlow gave similar feedback regarding the new engine.

Spies set the second fastest lap time at the test, 0.146sec behind Dovizioso.

"We worked on some things and got going pretty well. The main focus was on distance with the bike," explained Spies. "We got a decent pace going, especially with lots of laps on the tyres. I was happy with what we tested so now we go to Aragon and try to keep going forward."

Lorenzo was eighth quickest.

The Aragon test takes place on Wednesday.