Hey Motoartur.
As you've seen on a different thread, there is much debate as to the avaliability of unleaded fuel. Now, to your questions:
1. Changing the pipes to a non cat version would be my recommendation, since we cannot know for certain that unleaded is available everywhere. However, I know of two danes who are doing the west route on new Z's and decided not to change pipes. I am unaware of their whereabouts currently, but the last I heard, they reported no problems at all. So it seems not to be a problem. My recommendation is purely based on a "better safe than sorry" principal.
2. I personaly did not disconnect the lambda. Prior to my trip, I disconnected the wires for the lambda to see the difference in fuelconsumption, in case it failed during the trip (I did not remove the actual probe. Just disconnected the wires plug). On my, admitedly brief test, I could not detect any noticable increase in consumption. Possibly 1km less per liter. But that may be caused by a different driving style that particular day. I've had the lambda tested when I got back, and it is working like intended. No residue from leaded fuel could be detected. Which again leads me to believe that it is doubtfull that I ever ran it on leaded at all.
Please note, that having a cat in your pipes is mandatory in most western countries. Idealy, you should wait to change your pipes untill you reach the country/countries where it is allowed to run without catalysts. Both you and I know that this isn't going to happen
. Setting enviromental issues aside, I find it highly unlikely that you will run into problems with police anywhere because of catalyst free cans.
As for the low quality, all I can say is that I had no problems running on what was available during my trip though Africa. This being from modern pumps in Morrocco and SA, 30 year old underground tanks in Niger and Mali, and roadside sellers of petrol in coke bottles in Gabon and Congo. I do beleive that I bought a particularly low grade batch of petrol some time in Mauritania, where my mileage dropped to 17 km/l. Where I'd usually do around 21-25 km/l. It is the only reason I can think of to explain the sudden increase in fuel consumption. However, this was the only tell tale sign. The engine ran as smoothly as ever. Whether the engine has taken damage from this, I ofcourse don't know for certain. It's been over a year since my return, and I would imagine that any damage on the engine would have manifested itself by now. Running the engine on low grade/octane petrol for extended periods of time, may however be a different matter. I refer you with great confidence to Kev on this matter.
Uhmmm...does the Z even have a fuel filter? I'm unaware that the R does. The only ones that I had on my R were the ones that I fitted when I fitted the extra large tank from OTR. I changed them once on my trip. I only did this because it seemed like the right thing to do, rather than out of any necessity. They actually looked fine. Same goes for the airfilter.
Hope this helps.
Best regards.
Torsten