Don't know what the problem is...I just type XS400J, and get all sorts of hits. Try leaving off the Maxim, or type 400 Maxim, and leave off the XS400J. I picked up a new manual (circa 1983) on Ebay. I rebuilt a crashed '83 XS400J searching parts on Ebay. The single hardest part to find, was the right-side outer battery cover.There are lots of Maxims out there. Try this link for parts referencing. (it's the first link to appear via Google using xs400j parts)
http://www.boats.net/parts/search/Yamaha/Motorcycle/1982/XS400J/parts.html