The lemon law is more myth than a law, It is bassed on the old days where they did buy backs but it just does not happen any more and they get past the red tape of it all due to the number of quality check points during manufacturing. The only problem is they are still done by humans and that leads to human error. Have you tryed taking it to an other merc dealers cause it sounds like human error in trying to fix it rather than the motor being a lemon. What worries me is if the can come to the conclusion that it is starving for fuel why can they fix it, there is not that much in volved in the fuel system alone that over three trips there they have not covered all bases.