The anti dieseling device is a solenoid so it needs power to operate. It needs this power whenever the ignition id 'ON' but at no other time.

The purpose of this device is to allow a spring loaded 'needle' to plug the idle circuit whenever the engine is turned off. Even if the plugs are glowing white hot, this device cuts the flow of idle fuel to the engine & it can not 'run-on' without fuel.

It also prevents unburned hydrocarbons from entering the exhaust system, to be ejected into the atmosphere on the next startup.

If it is disconnected, the idle circuit is closed & it is necessary to increase the idle speed so that the engine can draw fuel from the transition port. This fuel is calibrated to be mixed with the idle fuel for correct mixture, but without the additional fuel from the idle port it is running lean, & therefore, badly.

I have been using a stock carb on my 1200 for years & I love it.
It is correctly sized for smooth running, great economy, & peppy performance without being over the top.

Those clever little Datsun engineers definately knew what they were doing when they designed these.