Why does my 225 run so rough cold?

I too would suspect choke. you maybe able to test if it is a choke problem by manually adjusting the choke when its cold and see if you can get it to run smoother.

I've recently read the carb chapter in the stockel book dan is recomending above and compared that with my carb manual and carb rebuild guide. This along with rebuilding my carb a couple times to get familiar with its mechanical parts and connections/movements and troubleshoot along with a bit of just plain playing with the carb has taught me a lot.

point being, Dan has good advice above, I'd really recommend reading that very accessible Stockel book (at least chapter on carbs), plus I recommend some manual experimentation with the choke

Where to start: manually open and close the choke by the choke shaft. but dont put your hands in the carb bowl... explosions occur down that hole and they dont always stay down there like they should