[quote=George;111626][quote=Kev;85073]It will only correct the fuel mixture when the O2 sensor is in the closed loop, that is when you are mostly on the cruise & at lower RPM. Other then that it will run a leaner A/F ratio.

Hi Kev,
1/ I would like to ask what do you mean by "closed loop" function of O2 sensor. I assumed, that O2 sensor (lambda) is functional in ALL engine loads and speeds to correct the right A/F ratio - let say "feedback" from exhaust gasess O2 volume analysis - back to ECU, to correct the amount of injected fuel. Yes you are quite correct, the O2 sensor sends a 0 to 1 volt signal all the time the bike is running. The ECU only looks for the closed loop voltage signal only at certain times predetermined by these conditions, when the bike is at operation temperature , when you are cruising at constant or small throttle openings & below 4000 RPM. Could you advise the limiting of O2 sensor function depending on RPM, etc.?

2/ I suppose that O2 sensor is able to correct slightly changed A/F ratio (for example by snorkel removal), The O2 sensor is not a tunning device, it will lean out or richen up the fuel mixture trying to keep the A/F ratio as close to lambda control when in the closed loop.but the main issue for me is unknown "range", in which the O2 sensor is possible right correct the A/F ratio (in case of new cans, etc.) Answered above.

3/ What wil happen with the catalysator in case, that we will change the A/F ratio due to new cans, DNA, etc. - for example by tricking temperature senzor to run more rich fuel? In the open loop the bike will run lean with these mods, so a fuelling device is needed to correct the A/F ratio, we have had no reported problems over the past 5 years with any damaged Cat using these mods.

Thanks, Jiri

Thanks for all explanation, Kev!
I have to confirm, that O2 sensor is limited in function. A month ago, I replaced old coolant temperature sensor in my car (equipped with O2 sensor). I measured both old and new temperature sensors (thermistors) by different temperatures and the result was, that the old sensor gave information, that coolant temperature is much colder, then in reality. After replacing of the temperature sensor, I felt a huge difference in performance – especially by cold engine (= limited O2 function), when car was lazy and hesitated with old sensor due to rich fuelling. But by hot engine, there is a difference too, so I suppose, that O2 sensor was not able to correct the right A/F with the old temperature sensor.
I had 2004 XT660R with surging and jerking, replace of ECU (type 2005) helped a lot, but some surging remained. Now I have 2008 XT660Z and I must say, that the performance is quite different – smooth, no surging (only slight “jerk” by throttle opening in low rpm, typical for injected engines) and you can go in lower rpm with XTZ. But, I was surprised, when I changed my new XTZ with my old XTR on one trip with my friend, who bought my old XTR. The engine performance of XTR was really much more better in low rpm (we had the same feeling with my friend) and I think, that in high rpm, the XTR was slightly better too :-( The XTR had 22000km and XTZ had 2000km on clock. I think, that the new Euro standards are the reason. XTR had lower environmental standards (uncontrolled cat), so the engine was not as limited...
Thanks Kev!
Jiri