I have a 1998 WR400 with a Keihin Flat CR carb. While trying to clean the carb, the return action on the throttle started sticking worse and worse. I followed the arm down to the connection near the Accel Pump. There was a small crack in the black plastic arm. When I moved the throttle again the arm broke. I included a pic of the broken part. It is the black plastic arm that connects to the Accel Pump plunger rod, and also controls the spring for the throttle. I have looked extensively at the carburetor exploded view, and I cannot see which part this is. The diagram doesn't show that side of the carb. Please help!