We claim the ornamental design for a primary cover for a motorcycle, as shown and described.
The FIGURE is a front view of a primary cover for a motorcycle according to the invention.
The broken line showing of the environment forms no part of the claimed design.
The perimeter line in the drawing represents the rear-most outer edge of the primary cover. The rear edge of the primary cover occupies a single flat plane perpendicular to the viewer's line of sight.