2006 wasn't as good for him, but after he moved to KTM in 2007, he scored his first victory at the 2007 Catalan motorcycle Grand Prix.

He ends the 2008 season with 7th at Valencia and 17th in the final standings, four places behind the most successful KTM rider (Marc Márquez) in an unsuccessful year for the Austrian concern.

For 2009 Koyama joined the smaller Loncin team, alongside Alexis Masbou, and struggled to score points.

Koyama finished eighth in the championship, taking a best placing of second at the German Grand Prix at the Sachsenring.

After Roberto Rolfo parted company with Technomag-CIP at Grand Prix level,[2] Koyama completed the season with the team; in six races, he finished outside the points in them all.