Kostas, give that poor engine a break! A 11x6 is too much prop. Your .40la has the power of a .25BB engine, maybe. I have found that a 10X5 is a very good prop for the .40la. As for your problem with the fuel draw, do you have the tank placed close to the engine? If not, maybe the engine can't pull the fuel that far when the plane is held vertical.