Hey ex man. What did you use to determine the speed. I have a 99' 400ex and it will only do about 65 to 68. Not saying your wrong but that does sound a little fast for a stock 400ex. But don't mind me I have been mistaken before. Ride safe.
Mike

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My 2000 400EX will do 80 for real!! I ran it beside my best friends truck on the highway, looked in the window to see the needle at 85mph(only 80 though, looking at an angle will fool ya!!) it is all stock also. all i did was adjust the throttle to correct specs. seems to be a 00' problem. i bought it new so it must be a honda fluke or something. dang i got good luck!!! not going to the dealer for this problem!!