I was going through this exact same thing and I think I just found it! After sealing the carb,backplate,around the pullstart and replacing the fuel lines I got to looking more in to the fuel system and guess what?! The fuel tank was leaking around the lid even though I thought it was sealing perfectly. I'll order a new one next week but for now I'm going to try using some of that RTV stuff around the lid (after you unscrew that plastic piece holding the rubber ring on). I have it propped open (hope it doesnt stretch the spring to badly) to let it dry. I was noticing some air bubbles in my fuel line so I guess this would be the culprit? Anyone think this'll fix it? I'll go dig around my parts bin and see if I have any spare tanks or seals but for now I'm hoping this will do till I can order something new.