Good advice Guyfang. You need the TM for reference, pictures and descriptions are invaluable.
The fuel rack is the long stamped steel bar that sits inside the engine block, just under the metering pumps.
It connects the governor and fuel stop lever to the arms on the metering pumps.
It is spring loaded and has a notch under each pump to accept the pin on the end of each pump's lever arm. this is what controls fuel volume per stroke.
Because it is spring loaded and not directly fixed to the exterior throttle lever, ( in the "On" position ) if one of the pump's lever arms is frozen, the throttle and fuel shut-off levers on the outside of the engine will still appear to be moving correctly but the fuel rack inside the motor can be stuck in the off position.
It is only engaged by springs that push the fuel rack "ON" and a mechanical lever arm that pulls the rack back to "off" when the solenoid is disengaged.
Grab the TM here on this site and locate the pictures and you will then understand completely.