I have a 2004 Honda 250 ES that had set up for 2 or 3 years before I had purchased it. I have had the carb cleaned. It runs and shifts fine but will occassionally throw a flashing light in 1st gear (it flashes 10X) no matter which gear you are running in. It will continue to run in the gear that you are in. I can turn the key off and back on it will shift down to nuetral. Sometimes you may have to rock it to get it back to nuetral. Then you can start it up like nothing is wrong. Could it be an angle sensor or something else?

 

A guy i know his does the same in 1st and 3rd gear(s)