Why does the fuel gauge suck?
Well, I wasn't paying much attention to the first tank, since I was too busy getting used to the bike, and it was rainy and cold. But after that I noticed the gauge stayed on full for quite a while, then dropped like a rock.
When starting out the following morning (in the rain again), the range indicated that I had about 75 miles left on the tank, and the gauge was at about 1/8-1/4 tank. Then, as soon as we got on the Autobahn, the "Low Fuel" message came on, and the gauge was bottomed out! The Autobahn is much different than Interstates, in that the exits are few and far between, so I was sweating bullets. Plus, running out of gas on the Autobahn subjects you to a possible fine of about $300. Well, I went about another 30 miles before stopping, and it only took about 16 liters (a little over 4 gallons).
The next tank I paid more attention to the Range indicator and gas gauge. The Low Fuel message came on with about 60 miles remaining, and again the gauge bottomed out. And, once again it didn't take anywhere near 5 gallons to fill.
As much as I hate to run out of gas, I do like to know the real range of my scoots. So, once it warms up a bit, I'm going to put a couple of liters in the saddlebag and run her out of gas, paying close attention to the actual range she has and far I can go on "Low Fuel."
My Harleys all had the petcock that you had to switch over manually to reserve, but you knew how much fuel you had left at that time.
Hope this helps.