I have a pretty new Janome 6600. I had the same problem with the Regular 1/4" foot not being accurate. The gals on the Janome Blog helped me with that...Move the needle and even gave me the proper adjustment. The manual has some information but I had not read it carefully enough. The accufeed (built in walking foot) has a 1/4" foot too but I don't have that yet. It is ordered and I look forward to trying that out.
Judi