Suggest giving the powerful bikes like the Katana 600 better fuel efficiency, or at least a bigger fuel tank so you can buy a ton all at once. As it is they use up several times more fuel than the weaker version and you pretty much have to watch it constantly.
I don't mind spending more money on ethicol for a fancy bike, but having to fill it up every other day and not being able to go fast without burning up all the fuel in a second makes me sad.