400ex weak on top end

[lillbro11]

I have a 03 400ex with curtis sparks exhaust and rev limiter. 42 pilot jet and 155 main with k&n filter. Not quite the power I thought it should've had. Blows a little white smoke when cold and getting on it hard. plus lacking top end power.
What could be causing this?

[Trxman300]

im not to sure but my friends 250ex is going the same thing. blows smoke when getting on it hard from an idle and has an HMF full system and jets and my other friends STOCK 250ex has more power thru the ban.........canf figure it out either

[fmftrx300ex]

ur jetting is off

[Scro]

Originally posted by fmftrx300ex
ur jetting is off

Incorrect jetting won't cause it to smoke. White smoke means there is coolant getting through somewhere. You may have a blown headgasket.

[rooster300ex]

Originally posted by Scro
Incorrect jetting won't cause it to smoke. White smoke means there is coolant getting through somewhere. You may have a blown headgasket.

These are air-cooled motors.

The ol 400ex may need an overhaul if its smoking and its not makin much power

[Scro]

Bah...see what you get when you don't pay attention:p

[rooster300ex]

Originally posted by Scro
Bah...see what you get when you don't pay attention:p

Your not the only one. I've made plenty of mistakes myself

[riggsracin]

valve seals, cylinder worn,