Source: Associated Press When the MotoGP grid lines up at the Circuit of the Americas race this weekend, former champion Nicky Hayden will be the lone American in the field and he will not be aboard one of the factory bikes expected to challenge for the win. It’s a far cry from the golden era of American motorcycle racing, when U.S. riders won 13 of 16 world championships between 1978 and 1993. “The question wasn’t if an American was going to win, it was which American was going to win,” said Kevin Schwantz, who won the title in 1993. “This was a breeding ground for world champions.” Since then, Americans have won only two championships and none since Hayden’s title in 2006. “I feel some pride and responsibility to keep carrying the flag and representing our country until we’re ready to develop some young talent to come in and take my place,” Hayden said from his family’s hometown of Owensboro, Kentucky. Hayden and Schwantz hope a new series kicking off in support of the MotoGP races this weekend in Austin, Texas, will help rebuild the pipeline for U.S. riders to reach the top flight of motorcycle racing. The series called MotoAmerica is headed by three-time world champion Wayne Rainey, who is working to align its rules with international series, bring back regular TV coverage and restore the involvement of major manufacturers still recovering from a collapse in motorcycle sales during the recession. Hayden’s younger brother, Roger, is racing in the top class of the MotoAmerica series, and is serving as a roommate and mentor to 19-year-old teammate Jake Lewis of Princeton, Kentucky. “I want to be positive,” said Nicky Hayden, who made the jump directly from the old AMA series to MotoGP in 2003. “They’ve definably made a splash, and