Check your fuel line, make sure it is flowing free. Pull the carb and clean it out. How is the spark, strong?

 

I think "1bad450r" is on the right track.

 

The spark is strong enough to knock me to my knees when I grab it.
I will look at the fule lines and filters when i get home
Thanks

 

this is going on with my 400ex and i dont no wats wrong with it if u find out wats going on mind telling me

 

i havent gotten in the a carb on a 400ex but i recently fixed the same problem on a friends 426. the diaphram in the accelerator pump was barely riped and it made it run like hell. once that was replaced it ran like a champ. not sure if the 400 carb is anything like that since ive never really looked at mine.