This weekend’s Portimao Superbike race which marks the end of the 2011 season for World Superbike racing is also going to be the swansong for Yamaha that has decided to pull the plug from its official superbike efforts.  It will also be the end of Paul Bird Motorsport’s era as the official entry of the Kawasaki factory effort in World Superbike.  Paul Bird is looking for opportunities to stay in World Superbike with other manufacturers. Aprilia is touted as one of them while wild rumours even suggest that Paul Bird could become a privateer Yamaha entry.