Berta has a "double" tank setup. It's one tank but divided into two spaces because the main shaft running to the back in the middle of the tank. Anyway there are two lift pumps with some circulating hoses to level the amount of fuel in each space. I was trying to join 1000miles club recently and probably I could achieve that, but first bubbles of air was sucked into the fuel lines. I know that because when I was killing the engine it has a trouble to start again, I've needed to crank it much longer to start. So for now I haven't runned out of fuel yet. I'm a bit afraid because of this double pump setup. If it'll brake it will be twice as expensive as any other setup to fix.
