i have an 1987 trx250x. i had it bored .20 i run a k&n filter and a cobra pipe. i was wondering what kind of aftermarket carb i should get also what size and what size jets. i was thinking of getting a 38 pe keihin carb.

 

The stock 250X carb is a 29mm, which is large enough for engines up to 350cc (in fact, it's the same size as the 350X came with stock, only your 250X carb flows better!).

A larger carb won't give you any more hp or better performance.