Slight stumble when cold?

I adjusted the choke to one notch richer. It was on the second notch on the rich side from midway. Midway is the factory preset. Its on the third notch on the rich side now. Weird though its been fine for years. What causes all of the sudden for it to be off?

It should not change like that.
Do check for a vacuum leak or: cracked rubber hose ....
clean the throttle plates by the “throat” of the carb too.
It’s changed for some small reason.