I have a 1975 280z and when I start it it does not stay running for more than 20 seconds or so. I can rev up the motor or not still dies at the same amount of time. I need suggestions please.

Download the FSM and fuel injection bible from xenons30. Follow the diagnostics on the fuel system. It sounds like you already have an idea that you are starved for fuel.

You should give more details. Car dies after 20 seconds doesn't tell much. At least you mentioned the year. Is the car new to you, did you just work on it, did it run before, etc...?

75s have a fuel pump switch in the AFM, that closes when air is flowing. It's bypassed during starting. You can read about in the Engine Fuel section of the FSM. Sometimes they'll get some crud in the contact and break the connection. It's behind the black cover on the side of the AFM.

SteveJ didn't mention it but the link to the FSMs is in his signature.