I have an '81 Evinrude 4.5.Hadn't been run in years.A month back I changed the old impeller then tried it in a test tank.She started right up and ran real nice.But it couldn't be that easy.As soon as I launched the boat 2 weeks ago.Engine starts ,runs for maybe 5 or so seconds then dies.Checked screen filter on fuel pump,replaced clamps on fuel line.The odd thing I notice is when pumping the gas bulb it never gets hard.Could there be a bad check valve there that might cause the motor to die?Any Ideas are appreciated.