Okay, I'm completely baffled on this one. To make a long story short, my 06 KX250F lost all the radiator fluid and almost siezed. I shut it down when I realized what happend but it was too late. I superheated the bike. Piston and cylinder were shot and the exhaust valves were pitted. A shop replaced the valves and I replaced the cylinder and piston with a Athena 290 kit (why not, right?) I adjusted the valves and put everything back together and it fired right up. I test rode the bike and was super pumped on how well it performed with the 290 kit. About 20 minutes into the ride, it just died like the fuel was off. No luck on starting it right away but after 5 minutes, it fired right back up. 10 minutes of riding and it just died again. It did this about 3 more times while making my way back to the truck. Always fired up after 5 minutes or so and ran great until it just died again. I figured the carb must be dirty so I pulled apart the carb cleaned it and put it back together. I test rode it again and the bike was great, chugging up hills, snappy power, then it just died. It fired right back up this time, ran, then died. Spark plug was a little white and since it seams to die at low RPM I richened up the pilot air screw. Didn't help and was actually worse. I leaned the screw 1/4 turn and didn't help and was still worse. Now the bike won't stay running for more than a minute, but fires right back up after it dies. There has to be something that I did that would be causing this. I didn't touch the electrical system so I can't imaging the CDI would be toast already unless it is just a coincidence. What kills me is how well the bike runs right up until it dies so there are no symptoms to go by. Any help would be greatly appreciated. Sorry about the long thread but I wanted to give as much detail as possible.