Have 2 gasoline inputs to my walbro carbrator. The

Sounds like you have the lines connected incorrectly. Make sure that the bottom of the carb is connected to the inlet side of the primer (take the lines off and with one of the ports covered with your finger push the bulb, if it collapses and doesn't return then that's the suction/inlet of the bulb). The other side of the bulb needs to be connected to the gas tank. The other side of the carb needs to go to the filter side of the gas tank.
Good luck!

hello sir, fuel line routing for ryobi,poulan trimmers, looking at machine from left side,front green line from tank to bottom of port on primmer bulb. rear line from tank which has filter inserted through tank with small white ring pushed up aginst tank & filter fittings, goes to port at bottom of carburetor.top line from primmer bulbgoes to top port of carburetor. that is the way thay go on.it is important to make sure you have the same fuel line I.D. and O.D. are very important! also if old line dissolved it will get in carb. and clog ports & small screen inside.clean inside of carb. with carb. cleaner & air pressure. to get your parts and numbers ,go to mtdparts.arinet.com, parts,791-683398,fuel line assembly.hope this helps,MrFixIt, oh could you please rate this solution,thank you.. this is for most fuel line trimmers~~~