Athena (P400485100032) 83mm 290cc Big Bore Cylinder Kit Yamaha WR 250 X 2008-2013; Yamaha WR 250 R 2008-2013 Athena's Big Bore kit brings the raw power you have been missing in an easy to install, reliable package that bolts on with no machining needed in most cases, and includes easy-to-follow step-by-step installation instructions