if it smoked more after changing the valve seals. you may have got them on the wrong valves.
example. exhaust seals on intake valves and vice versa.
not sure if the 400ex seals are one side only like that but it happened when i had the heads on my truck done after it bent a valve. the guy who did my heads put the valve seals on the wrong valves on every cylinder and it smoke like crazy.
might be something worth looking into.
04' 400EX
White Bros. E2
FMF Hi Flo Headers
DynoJet Kit
K&N Filter
Hot Cams Stage1
EHS Racing Air Box Lid
DG Fat Series Nerfs
Pro Armor Swing Arm Skid Plate
Pro Taper Bars
Maxxis Razr's on Douglas Wheels
Pro Armor Foot Peg Maxi-Mizers
ASV C5 Pro Clutch Lever
LSR P-Brake block off
Modified stock carburetor
Sparks +6 key