Yea it fires right up. A few times it has died right after starting but restarts easy. I don't really feel any loss of power. Acceleration right up to the rev limiter is smooth, enough torque to easily take off at 1100- 1200 rpm, I often don't even have to use the clutch when I come to a stop sign unless there is other traffic and I have to actually come to a complete stop.
The miss is very noticeable audibly, and the drop in gas mileage is troublesome.
You said the data showed a lean condition. could this be a bad injector?
Unless the O2 data is flat-lined (around 400 or 500 Millivolts) OR unless it stays very high or very low ALL the time, then we have to assume the cause is NOT the O2 sensor.
In your case, we have to keep in mind that a lean condition on O2 sensor (for certain period) is only the messenger (or symptoms) of something else being wrong.
So, fact we have an Engine miss, combined with higher fuel consumption would be 2 symptoms and the O2 lean sensor data is just one more data point. Motronic EFI may be trying to compensate for a lack of fuel reaching / coming-out of injectors.
In addition to not being on-site to see and ride it, we have other limitations to troubleshoot these K1200LT engine issues:
A) These Motronic are fairly old EFI technology designed in 1980-1990 and do not furnish as much data-points to GS911 as the newer EFI from BMW (newer means since 2005 in "frontal-4-cylinders", R1200 and K1600).
B) When Motronic compensates because of a lean or rich condition, we do not have access to compensation values used as you have on newer EFI (or ODBII on cars).
C) Because of above limitations in A-B, to avoid chasing too many possibilities, we have to use a combination of:
- how does it respond and "feel" in various conditions (hot, cold, accelerating...)
- has the fuel-mileage change lately
- what recent work may have cause a change
- what common issues exist on K1200LT engine that are common and probable causes
The GS911 data, plus your feedback is a starting point to avoid too many traps and too many "change this part", then more trial of "change this other part".... until you finally find the cause (process of elimination). Some dealer will make you a nice bill trying many things....
CONCLUSION: for the moment, with limited info I have from your post and GS911 data, I would guess the most probable causes would be, from easier to harder to test / fix:
1) Dirty Injectors: you said bike not used much, stored for a while, old gaz... so may need some fuel system cleaner like Sea-Foam / Techron and a very good high RPM ride to clear it up.
2) Intake air leaks (common on K1200 as they age and is covered in many treads here in forum - not easy to fix as many parts need to be removed to reach as-far-as under throttle-bodies)
3) Defective / shorting / damaged spark-plug wires (common issue with age and need a wet test in the dark to confirm - would cause engine misfire but not a lean condition)
4) One or more Defective injectors (we cannot get confirmation from GS911 or Motronic on this - the EFI system just use "injection time" as programmed expecting the injectors to work)
5) Intermittent or worn TPS (not common as this specific TPS from BOSCH has been very reliable on R1100/R1150 and K1200)