MotoGP world champion Casey Stoner of Australia set the pace Tuesday as Honda riders dominated the opening of a second round of pre-season tests on the new 1,000cc bikes at Sepang. A month after topping the field here 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. Stoner, whose fastest lap Tuesday was 2 minutes 1.761 seconds, said he was pleased with the extra bit of torque and traction on the new bike. MotoGP is switching this year to 1,000cc engines, from last year\'s 800cc bikes. This week\'s three-day testing, which follows a round of trials at Sepang earlier in February, have given top riders their first chances to cut loose against world-class competition and make adjustments to their machines. But Stoner said an afternoon downpour frustrated his hopes of sorting out a problem with chatter in 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-2.0 minute lap time in the first tests here in early February despite recurring back pain stemming from a previous injury. His teammate Dani Pedrosa of Spain was second Tuesday with a time of 2:02.005 followed by rival countryman and Yamaha rider Jorge Lorenzo in 2:02.436. Lorenzo\'s teammate Ben Spies was fourth at 2:02.819 while American Ducati rider Nicky Hayden was sixth at 2:03.132. Hayden\'s Ducati teammate, multiple world champ Valentino Rossi, logged an eighth-best time of 2:03.245 and later complained about track conditions. \"It was a bad day. The condition of the track was very slippery because there was a car race last week,\" the Italian said. 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 ago, the new 1,000cc machines were noticeably quicker than last year\'s 800s, sparking some concerns from riders over safety. Testing ends Thursday and is followed by a final three-day session at Jerez circuit in Spain beginning March 23. The season officially starts April 8 in Qatar.