I want to start raceing dirtbikes?

You don't say how old you are but racing 2 strokes is fast becoming a thing of the past unless you happen to be a junior as they still have a section for the 125cc or one of the younger ones on a 65cc or 85cc as they are still a very competitive option. But for everyone else only those who really don't take their racing all that serious can be found still racing 2 strokes. Then you get to the other fact that if you are coming off a blaster the last thing you would want would be a 2 stroke 250cc as they can be difficult for even the better riders to race sucessfully. You would be much better off with any of the known brand 250f's.