My advice is to replace that carburetor with a good used one.

Yes, the rod is removable. It is staked in, so it is tricky. Perhaps you can buy a new rod from nissan or maybe straighten the rod. Maybe lubricate it, I do not know.

I've never been able to fix a Datsun carb that had that problem. If the rod sticks, it allows fuel to pour through the carburetor via the power valve all the time. Normally this should only occur at full throttle. If the top gasket is torn or the top is warped the same thing occurs.