Factory Yamaha's Ben Spies says there is still more improvement to be made to his YZR-M1 depsite only being just over a tenth of a second slower than Casey Stoner on day two of the Sepang MotoGP test.

The Texan lapped at 2'01.052 today, beating his time from yesterday and finishing one place higher than team-mate Jorge Lorenzo, but says his team is now adjusting the balance of the bike to see if more speed can be found on the final day.

"We got going pretty well in the morning, then even when the track started to slow down the pace was still really good. We started to mess with the balance of the bike a little today and played with the electronics to find a good foundation with the bike. At Valencia we compared some stuff and got in the right direction. Now we're here and taking the next step, trying some things to see how it affects the set up. There's definitely some room for improvement and some areas we're not struggling with at all," said Spies.