Raise the front of the kart off the ground and remove the wheels. Next, disconnect your tie rods (one end of each will be fine). Turn the steering wheel, and feel for stiffness. If it is stiff, the bearings, bushings, or whatever other pivot methods yours uses, need attention. A good greasing might do it, but inspect for excessive wear. Disassembly will produce the best results. Now, swivel each spindle by hand, and follow the above protocol.