2009 White n red XTX, with Quill Evo2 cans, K&N stage 1 filter, and snorkel removed - that's how she was was kitted out when I bought her.
She runs real good at anything above say 5-10% throttle, pulls really strong from low down. But at slow speed and light throttle, especially in traffic, the glitchy fuelling became apparent.

Once I found out how to get into the diagnostics, I discovered the CO was set to 26, but never knew what the standard setting was. That sounded high to me, so I reduced it to 20 and immediately found a huge improvement in traffic. Tried further reductions to 17, 14, 12, but it made little further difference, it's now back up at 18.

On advice from local Yam dealer tech, I bought and refitted a snorkel, but it made things worse, not better! (That was before I discovered XT660.com!). The standard snorkel robbed the upper end of power (couldn't breathe properly). I subsequently modified the snorkel by shortening the intake and outlet lengths. The first iteration made the surging worse whilst still robbing top end, the second iteration (really short) has restored top end and cured the surging. I'd like to think the ultra-short version now fitted cleans up the air flow into the airbox, but I guess that's still open for discussion.

TPS was originally set to 16 at closed throttle - this was increased to 19. Apparently this should richen the mixture slightly, but it also means the closed-loop fuelling mode is exited earlier than standard at lower throttle openings.

Overall, the above mods have made a big improvement to the low-end response, but once out onto clearer roads the performance is excellent - I'm loving this new addition to my garage!!

Latest mod has been to add a Nitro-X fuelling module (similar in principle to the Kev mod) but I haven't had the chance to play with the settings sufficiently yet to determine the optimum value.

I shall be very interested to hear how you get on with the O2 eliminator mod!

Bit more background and some pics are in my introductory post here: http://www.xt660.com/showthread.php?t=19581

Cheers!
Dave.