It would have to be a problem with the sending unit or with the speedometer. About the only thing I can suggest is shaking the bike left and right to try to jar the float loose.
If that doesn't work here's some reading on a search for "float" in the Tech and Performance and Cross Roads / Cross Country sections:
Please note that I added the link instead of trying to dig the answer out of the discussions because I'm not sure what you've tried but I'm pretty sure that your problem relates to one or more of the posts.
Retired USAF, IYAAYAS!
2008 V-Star 1100 Custom Bobber project
2011 Crimson XR with Forged Highway Bars / Hard Bags / Passenger Backrest, Ness parts including Smooth Layback Plate Frame/Mount / Rad 3 Mirror / deep cut grips / drivers floorboards /shifter peg / brake peg / passenger pegs. Witchdoctor black rack, Lloydz filter / timing wheel / VFC III, 7Jurock windshield, Drag Specialties seat.
Last edited by ammo_umb; 05-29-2012 at 07:17 PM.