There are some indications when you are taking too much l-mthylfolate. They are (as taken from this site):
Dr. Lynch advises to back off for a day or a week and then start back up slowly.
So far, mthfr.net is one of biggest resources I have found, along with several smaller resources. Does anyone know of any other good sites that offer insightful (not crap-shoot) research and information about this mutation?