Jorge Lorenzo and Ben Spies say they have been buoyed by a positive three days of testing for Yamaha.
Though neither rider was able to dislodge the works Honda riders on the first and third days, they were comfortably fastest on the second day, when Honda sat out after discovering an engine issue.
Lorenzo said he focussed on race simulations on the afternoon of day three, showing good pace despite the rear tyres dropping off more quickly than was the case on last year's 800cc bikes.
"Well, this afternoon was one of the hardest race simulations of my career because the 1000 is more tiring to ride and the rear tyre seems to drop a lot after three or four laps," he explained.
"After this the feeling stays the same but it's very different to last year, it's almost like racing in the rain trying to control the rear in the corner exits and acceleration.
"I managed to finish the simulation with a good pace so all in all it has been a very positive test, thank you to Yamaha for their hard work."
Spies, fastest on day two, could not improve on day three after a small crash early on.
He said Sepang had convinced him of Yamaha's potential, and left him full of confidence before the third and final test at Jerez.
"Today was good," Spies said. "We unfortunately had a small crash but we learnt a lot and got to test some new electronic settings which were a big improvement.
"We also tried some different shock settings which were a big step forward. It's a shame we crashed but we know from this test that the bike has great potential so we can go to Jerez with confidence."
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