The ornamental design for a kartbody, as shown and described.
FIG. 1 is a perspective view taken from a front, left side of a kart body according to my design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
Throughout the Figures, where shown, the dashed lines are included for the purpose of illustrating portions of the kart body which form no part of the claimed design.