My 400ex smokes when I first crank it everyday untill it warms up. Is this normal? I just recently rebuilt the engine and I was having carb problems and now this is the only issue im having.

 

What kind of smoke? Oil smoke?

If so did you rebuild the head? Did you mic the guides and valves? If so what was the clearance? Did you put new guide seals on it?

 

Doctorturbo is asking the right questions. Sounds like valves.

 

I had the valves installed at a machine shop, and I did have new seals installed. the smoke smells more like fuel.

 

Well that could be a lot of things. If it's fuel the floats could be set a little high or trash in the seat or even a little nick in the seat so when it sits it runs a little gas in the intake and into the head and cylinder.

Does the oil smell fuelly? Does the engine use oil?

The first thing you need to figure out is if it is burning oil or fuel. I don't really know how to tell you how to do that other than smelling it.