I little while back I was riding my 2010 EFI TXC250 and was in the middle of a group ride. A dude was struggling on a hill and we were waiting, quite a while. Anyway when he got to the top we all got ready to go and my bike would not start. Was running perfectly. I finally got it to fire and it ran OK the rest of the day but not 100%. Every time it got cold it would not start. The issue was a $10 temp sensor that treads into the cylinder. The original one went bad at 1100 miles. Very EZ to install and cheap. Starts and runs perfect again. The EFI thought the bike was way hot when this happened and was not enriching to start cold and then did not run real good as it was compensating for what it thought was a real hot motor. Probably a fluke and not something you will run into but if your EFI suddenly does not want to start cold I would look there.