I've just done what I like to do to every bike I buy, which is sling a gallon can in a pannier, or wherever, and run the thing out of fuel to see how far one can safely go on on reserve, or with the fuel light on, or the gauge needle knocking on E, or whatever. So the warning light came on at 167 miles, and it started dying 45 miles later, which is more or less what I expected. I had the odd hiccup about 10 miles before that, presumably as the low fuel level sloshed back and forth over the pick-up. I had put exactly five litres in the can, so poured that in, and at the next filling station topped up the tank (and can). This time I put 5.5 litres in the can, and the total volume pumped was just 22.4 litres, which gives a tank capacity of just 16.9 litres. What? I mean, what? I thought these things held 20+ litres? Anyone?
