I just want to say we have never seen a XT burn any valves ever no mater what mods have been bolted to them, even running stage 1 & 2 filters + free flow pipes, with this set up I have personally Dyno tested the A/F ratio's & so did Freeze a Dyno expert from South Africa & the A/F ratios run around ratio 14.5 to 15:1.
But one thing I will argue about & I can prove 100% with Dyno results, at 15:1 the bike will not have the torque or HP compared to a bike running the exact same mods at a richer A/F ratio between 13.2:1 & 13.6:1. Yes the bike will run at 15:1 all day long but at a loss of HP & Torque.
My adjustable fuel mod corrects a lean A/F ratio from hard ware that has been fitted like free flow filters & pipes, the O2 controller corrects the lean closed loop A/F ratio. My fuel mod is a very simple fuel adjuster that does & have proven this so many times, it can correct the A/F ratio by up to 0.8:1 richer,
https://www.youtube.com/watch?v=glkdBO8aZm0 if you want the best tuning tools out there buy a PCV & get a custom Dyno PCV map at 6 times the price.
One other thing these XT's do not run rich with all the intake & exhaust mods, I challenge anyone to show me Dyno proof that they do as I have personally Dyno tested every version of XT660 ECU, every single mod ever bolted to a XT including all the big bore kit in varying sizes + stroker cranks + quite a few different cams?
Here is some data logging I have been doing on the latest KTM 1290's, I would love to see how the guys that bag my mods have actually measured & Dyno tested the mods A/F ratio's.
http://www.ktmsmt.com/viewtopic.php?f=29&t=6888&p=42781#p42781
MT09's
http://mt09.motorcycle-talk.com/forum/mt-09-modifications/1565-kevs-anti-throttle-surge-mod-25.html
I don't tune bikes with the seat of my pants I used the latest Data logging tools & reconfirm all my work on a Dyno, I spend around Oz$2500.00 a year on test mods & custom Dyno PCV maps for different bikes & can prove 100% what I say.
Also say that the XT660 ECU can learn is the biggest load of rubbish I have every heard, if you under stand the X'660's mapping & how all the functions of a XT's ECU works you would know 100% the man does no what he is talking about. The variable difference would be from the F/L switch trim inputs between the TPS/RPM & the intake pressure sensor/RPM mapping with the valuables inputs going to the ECU's, the ECU learns nothing it is has pre-written mapping & the variables are changed with in the mapping from the sensor inputs.