I recently rebuilt the petcock on my XJ, in doing so I noted that it appeared to be missing a piece, some sort of plastic spacer, pictured here from the FAQ:
It never had it, but didn't leak. Might have been the source of my fuel systems. I put a new fuel pump in and everything is pumping fine, aside from this drip....drip... (unacceptable) fuel leak. I am thinking of just sourcing a new petcock, but am having trouble finding the exact one that we need on eBay. Searches for "xj600 petcock" yields only petcock rebuild kits. I am sure that another vacuum operated yamaha petcock will fit, but don't want to just buy one and when I get it I see it doesn't fit or work. What do you guys think?