I've had a lot of K-bikes and never had a problem with the tank-based fuel sensor, but I think I might now.
My 2003 K1200RS (~56,000) just started indicating about a gallon less fuel than is really in the tank. The low fuel light comes on at about 155 miles and if I go another 20 then the dash gauge needle is dead on top of the "empty" line. However, a fill up will only take about 4.3 gallons, which from prior experience means there's another gallon left until really out. Based on fuel required to refill, I'm getting about 40mpg.
More interestingly, after a fill-up, the dash gauge stays on empty until I ride a quarter to half-mile, at which point it slowly comes up, and at about the point where it came on, then the low fuel light will go out again. The gauge will indicate a full tank, but I think that's deceptive since the fuel gauge on these bikes normally hang on "full" until most of the first half is used up.
I suspect this has to be a faulty fuel sender, but I'm puzzled as to the nature of the failure. This problem started after I began riding it again this spring (I was off of it only about six weeks) but not initially, and I had treated the fuel with Startron. Has anyone had a similar problem? Thanks.