I have a 2004 XR400. Having trouble with initial flat spot with the first crack of throttle. Knowing that it does not have an accelerator pump in the carburator. Want to know if anyone knows of a modification of the carburator to change over to one with an accelerator pump so I don't have that flat spot. If you have any solutions for me, please give me a call at (916) 479-5198, my name is Mark or reply to this thread. Thanks!