I receive a lot of questions and people that misunderstand the fuel shutoff systems on kubotas. This likley is the same across larger series as well but my specialty is B and BX tractors.
There are 2 types of fuel shutoff solenoids. PUSH and PULL
Lets start with the PUSH type. PUSH means the solenoid pushes the fuel closed. So when your tractor is off the fuel shutoff is in the open position ready to run. This system also has a fuel shutoff timer. When you turn the key off the timer activates the shutoff solenoid to kill fuel and stop the engine. The timer does its countdown and then releases to open the fuel shutoff and is ready to start the next time.
The PULL system is a little more involved. PULL means the fuel shutoff solenoid pulls IN to allow the rack in the injection pump to move to the open position. There are 2 coils involved in this process. The PULL coil and the HOLD coil. The PULL coil is a high amp coil that is activated when you turn the key to the start position. Once you release the key after the engine starts it is then the job of the HOLD coil to hold the coil in for the engine to continue running. When you switch the key to the off position the coil releases and pushes the rack back to closed position thus stopping the engine. The HOLD coil is a low amp coil that can be powered indefinitely without issue. The PULL coil will fry if held in too long. There are 2 wire and 3 wire PULL coils. Red wire is the hold coil, White wire is the PULL coil and if there is a 3rd wire it is black and is a ground wire. 2 wire use the chassis ground. In troubleshooting situations its not as simple as just putting hot and ground on the wires to activate it.
This is a basic description of how each system works. Should you have more questions please feel free to contact me.