I have been trying to get my Poulan 3400 saw to run. I have replaced both fuel lines...though I am not exactly sure where the vent line is supposed to go. Does it just run back behind the tank and sit there? Or is it supposed to hook into something? After replacing both lines the saw will still not pump any gas into the carburator. It runs great for a few seconds when I pour fuel directly into the carburator, but then, obviously, quits because it does not continue to get fuel. Any suggestions?