Don't want to tempt fate in any way, but mechanical problems have been pretty small to date.
Here's a summary for those with a mechanical bent who may be interested:
(A bit boring for everyone else)
First off, Beau's petrol tank started showing the first signs of a pinhole leak way back in Germany, or thereabouts. From the rusty patch where the front of the seat rubs against the rear of the tank.
We fixed that with some proprietary tank repair glue but it didn't last.
Not to be beaten, in Romania Beau performed some spectacular theatrics (reported elsewhere) just to get a free permanent repair to this problem. Good ol' Araldite was used this time and has been permanent so far.

Not to be outdone, a tiny pinhole leak appeared in Caroline's tank, also repaired with Araldite, in Palmyra, and still good so far.

There have been a couple of oil leaks on Beau's bike. A minor one from a bolt on the cam-box cover which is set in a large rubber grommet. Cleaning and refitting this had no effect so a little silicon was needed.
More inconvenient was a leak from the clutch cover joint next to the oil filter which eventually covered Beau's right boot in oil. At least it should be waterproof!
We had two options here. To remove the cover, (we have a spare gasket) which would require removal of the exhaust, oil cooler and other stuff, with the chance of finding abused screw threads in the process and the old gasket requiring a day of careful scraping to remove. Or, apply a little two-part epoxy to the leaking area after cleaning. So we did the latter and it worked. It will need cutting if the clutch cover ever does need removing.

Beau's older and less-prepared TTR has had two roadside problems requiring the rapid location of a place to stay for the night. Both in Turkey.
Firstly, during a day's riding, the tickover became faster and faster until it became a serious danger to the engine. Closer roadside examination showed that the position of the throttle spindle in the carburettor no longer bore a direct relationship to the engine speed - something inside had come adrift. Fortuitously we found a good campsite nearby, with room to remove the carb. I suspected the little screw holding the throttle slide lever to the spindle had become loose and hoped it was nothing worse.
Removing the carb meant removing:
All luggage
Rack and panniers
Seat
Tank
Airbox
Subframe strut
Not a small job like the 'old days'.
Dismantling the carb revealed with some relief that my guess was right, the screw just needed tightening, with some Loctite for peace of mind.
But there was evidence of some earlier butchery in there, a float support had broken at some time and been repaired with Araldite which had damaged the seal on the outlet of the accelerator pump. The gasket itself was also broken. There had been a damp patch of petrol there for a while, and after fitting the carb back twice the best we could do was to fix the leak at the pump, but leave a leak on the lefthand side of the float bowl. This only makes a damp patch if the bike it leant on the sidestand with the petrol left on.

Not long after that we had the problem with Beau's rear tyre going flat, for no reason that we ever found. Must have been some dirt stuck in the valve when it was pumped up.
At the end of this piece we'll leave a couple of questions that we'd appreciate answers to - please.

Caroline's Serow is running too rich, OK at sea level and thereabouts but a problem at 3000ft and we have higher to go.
We lowered the needle in Palmyra (removal of carb a similar job to Beau's TTR), but only a small improvement resulted. And we have little chance of finding a main jet of the required smaller size. But we have stranded copper wire and a mini gas soldering iron. Info needed, see below.

Tyres: a perennial subject for discussion on these sorts of journeys.
I have Continental TKC80s, regularly recommended. After 5500 miles on tarmac both are less than half worn, a bit surprising, and I'm carrying a spare rear. When I fit that in southern Egypt the existing one will probably be good enough to go on Beau's bike, saving a bit there.
Beau has Trelleborg front and rear and as far as I can see they have nearly as much tread now as when we left Dover. They seem to deserve their reputation. So the front may last right to Kenya.
Caroline has Pirelli MT43 on the front, pretty worn at the start and now, marginally, an MOT failure. So it will last to Cairo or southern Egypt no problem. But will need changing before Sudan.
The rear is MT21 and is still OK, more tread than Beau's rear tyre, and may last a long time yet. Will have to decide in Cairo whether to change it or not.

Chains:
As expected, entirely dependant on how religiously you oil them, and we have been travelling part of the Holy Lands.
So mine hasn't moved at all (without actually using a ruler to measure the free play) - no adjustment needed.
Beau's has been adjusted up one notch on the snail cam.
Caroline's has not needed adjustment.
So more regular oiling needed for certain chains, but we're approaching the Sahara and there's endless debate about what to do there.
The most respected advice seems to be:
No oil at all - nothing - but regular meticulous cleaning.
Well, that'll slow our progress even further...... we'll look out for the walkers.

So, question time.
1.
Why is it, as we discovered with Beau's flat tyre, that the nut on the valve stem, which should always be loose, always tightens itself up, whereas the nut on the security bolt, which should always be tight, always comes loose??
After all, they are both in exactly the same position on the wheel rim!

2.
A 2002 Yamaha Serow with a carb from a 1990s model, has a main jet of 105. It runs fine at sea level and up to say, 1000ft, but above that runs rich, and at 3500ft is maybe 10mph down on top speed. Plug is black and sooty. The needle is in the lowest position.
How many strands of wire from a piece of flexible 5A elecric cable should be carefully inserted into the hole of the main jet, soldering them onto the end of the jet to keep them in place, to get the correct mixture for about 8000ft altitude??
Sorry, we don't have a micrometer to measure the strands of wire.

All answers will be carefully considered, including any in Arabic.