TM 33 Flat Slide
Sorry I didn't reply to your ealier question. I'm not very good at checking back on threads.
I bought a flat slide cheap on fleabay and bought the adapter from Enduco at XT225.com. I am not great at jetting and even with my limited talent it is a heck of a lot better than stock. Fires right up even when cold and has good roll on the throttle power. I also have a ProCkt pipe made for the TTR225. If you go for the TM33 you should at least do the exhaust mod.
Good luck, they are a great light weight dependeable bike.