SEPANG, Malaysia - MotoGP world champion Casey Stoner set the pace as Honda riders dominated the opening of a second round of pre-season tests on the new 1000cc bikes at Sepang.MotoGP is switching this year to 1000cc engines, from 2011's 800cc bikes.A month after topping the field in earlier tests and two weeks after becoming the father of a baby girl, Stoner returned to the Malaysian circuit to emerge fastest again as riders battled a slippery track and tropical heat. His fastest lap was 2min1.761; he said he was pleased with the extra bit of torque and traction on the new bike.'STILL CHATTERING'The three-day test session follows a round of trials at Sepang earlier in February to give GP riders their first chance to cut loose against world-class competition and make adjustments to their machines.Stoner said an afternoon downpour frustrated his hopes of sorting out a problem with chatter on his bike. "No change in the chatter problem. Today was a little bit of a waste of time," he said.Stoner was the only rider to set a sub-two minute lap time in the first tests in early February 2012 despite recurring back pain stemming from a previous injury.BAD DAY FOR ROSSIHis team mate Dani Pedrosa was second with 2min02.005 followed by Yamaha's Jorge Lorenzo on 2min02.436.Lorenzo's team mate Ben Spies was fourth on 2min02.819 and American Ducati rider Nicky Hayden was sixth on 2min03.132.Hayden's Ducati team mate, multiple World champion Valentino Rossi, logged an eighth-best 2min03.245 and later complained about the track. "It was a bad day. The condition of the track was very slippery because there was a car race last week." Pedrosa claimed some progress in chassis set-up and engine management but also complained the tropical heat made riding hard.During the first tests four weeks earlier the new 1000cc machines were noticeably quicker than 2011's 800s, sparking some concerns from riders about safety.Testing will end on March 1 but be followed by a final three-day session at Jerez circuit in Spain from March 23.The season will start on April 8 in Qatar.