Careful running the 250ex without the airbox lid, it leans out real easy and you can do damage to the motor.

 

What do you mean "leans out?" I haven't heard/felt a difference other than maybe less throttle delay since taking it off, other than that I can hear the sound the filter/airbox makes better without the box on.
*EDIT* I also heard that if it backfires after running at high RPMs after a straight or something, that it is too lean, and I do have the option to change the jet that isn't the long pointy one (lol @ that description) up to 105. Currently I went from the stock 95 to the new 100 and can increase to 105.

 

The 250ex doesn't like to run with too much air, it runs lean very quickly. Your main jet is not "a long pointy one". On the 250ex the main jet is a button style as opposed to a hex style. It is located on the bottom off the carb in the float bowl.

 

Ah ok, btw, by the description I gave above, does it seem like it is running with jets that are too small or too large?