You may want to check you jet needle setting, usually is set on the 3rd gap. The lower the setting the richer it will burn. if you are in fact burning rich, try setting your needle up one notch. You could also be not getting enough fuel at 3/4 to full throttle and that to will give you a bogging (fuel starving) symptom. Then you may want to check you float level. Clean your airfilter and then run with your airbox lid off and then with you lid on. If it runs better with lid off then your rich. If better with lid on then your lean. This should get you started in the right direction.
2001 400ex
AC Pro peg nerf bars
AC Bumper with mud screen
DG A-Arm, Swingarm, Full skid plates
Outerwears red shock covers
Dynojet kit (currently 165mj)
42 piolet jet
K&N filter w/precharger
FMF Powercore IV-2 S/A
Ported headpipe
No air box lid
Custom graphics
Custom storage compartment
1 Crazy Cracker
"Pain last for a little while,
Humiliation last forever!!"