2001 400sxc with dual sport equipment. Has Mikuni 40mm carb and is stock. The bike will run fine for awhile then acts like the choke is on and dies. The funny part is that sometimes it fires right back up and other times it doesn't? At first I thought it was the carb, but it has been apart a few times and never do I find anything wrong. I verified the choke is seating properly and float level is correct.The fuel flow is fine and the gas cap vent is open. Since this is kickstart only I can not verify any electrical problem if I can't get it to run. It always has good spark.The valves are in spec. This can happen when the bike is cold or hot. Maybe someone out there has had a similar problem and has some easy answer?