The ornamental design for an adapter for motorcycle fuel tank, as shown and described.
FIG. 1 is a perspective view of an adapter for motorcycle fuel tank in accordance with the present invention showing my new design in use threaded into a neck of a fuel tank;
FIG. 2 is an enlarged side elevation view of the adapter for motorcycle fuel tank;
FIG. 3 is an enlarged top view of thereof as viewed in FIG. 2; and,
FIG. 4 is an enlarged bottom view thereof.
The fuel tank shown in broken lines in FIG. 1 denotes the nature and environmental use of the design and is not part of the design.