Im a bit of a newbie but im fairly mechanically inclined so bear with me! I recently picked up this bike its a 2000 400ex. It has a twist throttle and K&N filter. Other than that it is stock. Previous owner says it burns a little oil (rings?). Never been rebuilt. The day i got it it wouldn't idle. Still doesn't. I rode it all day with no idle but other than that it ran great. It was smoking a little though. White smoke that i only noticed at start up. When i downshifted it would backfire sometimes. At the end of the day it died. It would start but still no idle and it bogs down bad in the middle of the throttle and will die on the top of the throttle. I figured maybe it fouled a plug. When i checked the plug (today) it was black. Put in a new plug and it starts easier but still same issues. I took off the carb. I checked everything out. The main jet is stock 148 and clean as a whistle. The flaots are clean and move freely. The pilot jet was stock 38 and clogged to hell. I changed it out with a new 40. The carb looks almost immaculately clean besides the dirty pilot jet. put it back together and it still wont idle and still bogs out. Oh and when i was in there i noticed the idle screw wasn't even close to touching the throttle. I turned it in till it was just touching. Once it was back together I tried turning the screw in with no difference all the way in. So thats about it. I would like to know whats wrong. I have a Honda Service manual. I'm gonna try and do any work myself. My guess is needs new top end. Thanks in advance for all your help!!!!