I have a Poulan Weedeater Featherlite Plus that will not continue to run. It seems as though the tank gets pressurized and when I open the gas cap there is a surge of air into the tank. I don't know if this is supposed to happen or not. There are 2 tubes into the gas tank from the carburetor. One is short and the other goes clear to the bottom of the tank and into the gas. I can pour gas into the carburetor and it will start and run for 5 seconds or so at full power then just dies out. HELP!!