Background: So i have been riding the last 3 weekends hard at the track. My 07 yz450f was running fine for the last 3 weekends and this past weekend, i recently took the carb out and cleaned it really good because it wouldnt idle for anything. put it back in and it ran like a champ . So this weekend it started smoking white smoke out of the valve cover vent tube. My dad was behind me on his YZ250 and he told me that my bike was smoking like a diesel so i put it up and ended my weekend early. i have been reading a lot of threads about possible coolant burning from bad head gasket. but today i went to talk to some mechanics from my local moto shop and they told to drain the oil and check if it was milky. i asked them if i should start it and warm it up first or just drop it and look at it, they told me to just drop it and see if it was contaminated. so when i got home just dropped it in a fresh oil pan, i could see some sort of seperation of liquids in the oil not terribly bad but still could see the difference.so i put some new oil in and started it to remove the rest of the oil out of it so it would be ready to replace the head gasket. Well i had it running not even 2 minutes into warming it up if just dies as if someone pushed the kill switch. now it wont start for anything i checked the fluids and the oil just looked the same with a slight discoloration of contamination and the coolant which was green-yellow is now blueish in my radiator. so my 2 questions are is it just a bad head gasket and thats why its smoking out of the valve cover vent tube, and did it seize up cause i can still kick it over with ease it just wont start. Please help me i just wanna get back on the track before the snow starts flying!!!!!!!