You got air into the system. You are going to have to use a vacuum pump on the bleed screw of the rear calipers to draw brake fuid through the system. As you do this never let the level of fluid in the reservoir drop below the minimum mark. Otherwise you will keep drawing air into the line. Keep adding fluid to the reservoir and drawing it off at the bleed screw until you eliminate all air bubbles. Then tighten the bleed screw and operate the brake several times until the brake pads are bedded. You may have to bleed the system more if the brakes feel mushy. Check out f650.com for detailed instructons.