I am sure some of you this but I just thought I would pass this on.
Many aftermarket CDI boxes sold for the 400EX are actually stock Honda XR250R boxes. The unmodified XR250 box will give you about 800 more rpm on top and a faster ignition curve. You can purchase this directly from your local Honda dealer and save money.
Order: CDI for Honda XR 250 1992-2004
Part #30410-KCE-671