JD 400 electric fuel shut off solenoid valve

[Jerry O]

My old JD 400 back hoe/loader stopped running yesterday because of no fuel getting into the carb. The electric solenoid fuel shut off valve that sticks out of the bottom of the carb was dead and would not let fuel pass. I stuck a piece of wire into the valve to hold it open so I could run the tractor into the shop. My question: What is the purpose of that valve? Is the valve necessary or can I just leave the valve in an open position and put a mechanical fuel shutoff valve by the fuel pump? Does anyone know where I can get a used valve? New ones appear cost a lot.
Any help will be appreciated,
Thanks, Jerry O