On XT225.com there is something about a replacement (read more power) carb that is available.
Since you're not afraid to tear into the carb on it, I'm fairly certain you've got the technical wherewithall to install this Mikuni pumper carb.
My goals for this project are as follows:
1) Increase responsiveness to short sudden bursts of open throttle
2) Improve cold starting, reduce warm up time and engine stumble
3) Augment overall engine horsepower and torque
4) Keep the bike quiet
5) Allow the bike to easily be returned to stock condition for resale
To satisfy the above I've selected the Mikuni TM33-8012 carb to replace the stock carb. The model 8012 includes an accelerator pump which should provide an increase in responsiveness