Good advice by CD'sCycleshop. If you'll be doing both, and since the front sprocket is easy to change, it might be a good idea to go with a 15/40 for the drags, and a 13 or 12/40 for the track. If you really want to do well at either type of racing, have your quad dyno'ed to find out what RPM yields the most torque, then put sprockets on to keep the RPM in that range. A lot depends on the track and the conditions of the track that day. I used to race dirt track go karts and would change sprockets quite a lot. We'd find out where to be during the heat races and then swap what we'd need before the feature race. A lot of it was done by the seat of our pants. WAG. (wild *** guess)

 

Yeah i don't want to dyno it until i get all my mods done that i want then do it all at once.Track conditions change a lot so ill probably be changing them a lot like you said also.

 

You can also swap out the cdi box with one from an xr250r. it will give you an extra 1000 rpm on the top and it will advance the ignition curve a lil bit. It also removes the rev limiter. Alot of aftermarket boxes are rebadged factory xr250r bosex.
Word of caution is that supposedly it makes for a hard start when its cold out. I have never had this problem with the xr box even in 10* weather but I might be the minority.