Just put a new piston in my KX450 and checked the valves. Went ok for my 1st time. But I'm getting lots of smoke out of the exhaust. White smoke. Went to the track today to see if it would burn off but its still smoking just as bad when I 1st started it. Like I said this is my 1st time working on a 4stroke. I don't know why its doing that and where I should start looking. Bike idles perfect and runs great too. No misses or hiccups. I tried the KX450 forum but that one seems to be pretty dead and I haven't received any responses in 3 days. Please help.