That could be a front tire slightly out of round, or having ridges/lips that actually change the local radius of the tire. My wobble is side-to-side, not up-and-down.

--Tom 02 TBA; 130 mains; TBS; Nology Coils&Wires;Unifilter/opened Airbox; -AI/snorkels; -2 baffles;Progressive 440s & Springs