Wow this thread is insane, 677 pages! I bought a 2000 XR400 this spring. I took it to a buddy of a buddy who is a full time mechanic out of his garage to go through the entire bike and get it ready for the season. He rebuilt the carb and it would start in 3 kicks every time cold. When hot its always first kick, even if I drop it it fires up in a couple kicks without the decomp. The more I rode it the harder and harder it got to cold start. I'll admit I did run ethanol gas in it. Since I have drained the gas tank and ran enthanol free only from here on out. I was assuming that was the cause. I took the carb apart last night and it looked pretty good in there. The numbers off the jets were 142 & 526 if that makes sense. It ran perfect before so the jets seem correct. I live in Boise so I ride elevations from 2500 to 10000. I got it to fire but it will not idle. I have messed with the idle adjustment screw so much I'm not sure where it needs to be, anyway to find that out? Seems like the screw isn't doing much, all the way out or in and she acts pretty much the same. Before I disassembled the carb I checked the lean/rich screw on the bottom of the carb and it was about 1-3/4 turns out. I set it for that which should be correct from the research I've done. Some people say you can go out to 2-1/2 but that should be max, anymore and a guy needs to rejet. I also noticed I do not have the "cone" or "skirt" that is the carb, its the yellow thing you should see right away when accessing the bowl. Any recommendations? Should I keep playing with the idle screw and the lean/rich adjustment? Maybe I should order that skirt thing? I'm not sure what it does but it ran fine without all summer. Thanks for your help!! Edit, Maybe I should buy the Pumper Carb from XRonly.com and be done? Its spendy but I have heard amazing things about it. If its a game changer it might be worth the $400 or whatever. Although I have read they are way more complicated, might be over my head.