2005 Honda 400ex blowing oil? (jetting too)

I have a 2005 400ex that is blowing more oil than normal. When i start it while its cold, it blows smoke that im pretty sure is oil! Also, every time i go riding (4-6 hours) It blows a little less than half a tank of oil. My dad says its the piston rings but hes no expert! Also anyone know how i should jet it for a k&n filter? (only because the previous owner had put bigger jets on it, i dont know why)

Is it blue smoke? With a K&N you are getting more air in, does it have an aftermarket exhaust? I would check the K&N website and see what they say about jetting specs with their filters. Keep in mind, it could very well be worn out rings.

* Added year and manufacturer to thread title.

No its white smoke! Thats why it doesnt seem too serious to me.

Oil smoke will look different depending on how much oil is being burnt. A little oil usually shows blue smoke, if you are burning alot of oil, and it sounds like you are, it will burn white and smell very strong. Could be piston/rings, could be worn valve guides/seals, could be both. I wouln't worry about the jetting until you get the motor fixed, if you mess with the jetting now, you will probably have to change it again when you get the motor running right. But generally you need to jet just a bit richer for a high flow air filter.