Gas tank problem starting

I have a 1993 Blazer full-size 2 door(looks like a tahoe but isn`t)350 5litre 4x4. I have just recently replaced a new gas tank with sending unit attached and also replaced tne fuel lines. When I attempt to start it, it starts for 3-5 seconds and them shuts off. I have put in about 15.00 worth of gas in tank.I also put a little gas in the carburator to try to start it but it still starts for 3-5 seconds and shuts off. Can you give advice as to what may be causing this