i take it its the new shape runner hyper ?as the old one has no key for the fuel cap.the barrel is held in ny a leaf which is part of the sliding mechanism for the lock so it only works with the right key the leaf holding it in tis the last one on the barrel and either needs to be dis assembled and access got to the bottom of the barrel from the side to push the leaf over and allow it to come out or you could use a slide hammer and pull it out this usually bends the leaf and it comes out but it could damage the rest of the cap.up to you how you do it mate.
adam bike doctor
April 2010