Two clutch friction plates were broken when I bought it.
Fuel enrichener piston (choke) seized in carb.
Trip meter was usually impossible to reset, due to not all the numbers agreeing to be rolled consistently.
Engine often stopped when the fuel level got a bit low. Later learned that the cause most likely was a restrictive fuel filter, but by then the bike was sold.
Front brake disc was worn dangerously thin, but opted not to replace it.
Splines on the output shaft holding the front sprocket were also badly worn, but only fitted new sprockets and a chain, and avoided lugging the engine to save what was left.
Previous owner had messed with the electrical system, causing some wires to come apart.
This was a XT600Z Tenere. I have every reason to believe the bike had rolled a lot longer than the speedo said, as everything other than the engine was worn or badly worn. This is also why I sold it instead of restoring, since it wasn't worth it, despite the engine that I loved.
So let's start with the engine. It needed 2500 RPM to run smoothly, and preferably 3000 or more in the upper gears. But it would run briskly between 2500 and 4000 RPM, and more than 5500 RPM wasn't needed even during quick passes of slower traffic. Perhaps one could get an extra HP or two by forcing it to rev all the way to 6500, but it brought mostly more noise. Insisting on pulling the 7000 RPM redline is torture for the engine and rider. I suspect the engine had been rebuilt, at least the top end.
The previous owner had replaced the stock air box with individual K&N filters, a change forced due to fitting the 30 liter fuel tank from the older model with its much narrower tunnel. I suspect these filters, or rather air disturbances at higher speeds, kept the top speed to around 75-80 mph / 120-130 kph under most conditions. Acceleration was very strong up to 60 mph / 100 kph, suggesting the power was there, but as speed grew, the engine ran less strongly. It could cruise all day at 70 mph / 110 kph without breathing hard, turning a lazy 4000 RPM in the process, a result of me fitting taller gearing than stock.
Oil consumption was mostly nil, then it would suddenly use a quart every 300 miles for a period before going back to zero consumption. Never found the cause, but I suspect a valve not closing fully for whatever reason - clearances were correct - because compression also dropped during the period of oil consumption.
The gearbox was fantastic, and one could shift easily up and down, with or without use of the clutch. Best gearbox I've ever experienced over more than 30 years of riding.
The engine vibrates, but they never annoyed me. In the most used range, 3000-4500 RPM, it is smooth enough to render mirror images clear.
With a 30 litre tank, the range should be 600 km before sucking fumes, but trouble usually set in around 450 km with the carbs running dry. Parking it for a couple of minutes allowed us to carry on again as if nothing had happened. For a while, at least. Refuelling was a more permanent fix.
The seat, after I filled in the section the short-legged previous owner had cut down with hard foam, was very comfortable, and allowed long stints. Leg position was superb for my sore knees, but most would probably want them further back and perhaps a bit higher. The huge fuel tank made it very difficult to stand up.
Suspension was the biggest disappointment for me, being both soft and harsh at the same time. Both ends failed to react to most bumps, as if compression damping was too hard. Larger bumps were absorbed better than small ones. But bouncing it at a standstill, it felt very soft. I tried 2.5W synthetic fork oil as well to no avail. Most likely, everything was worn out.
The front brake was weak, but it's hard to judge, since the disc was worn to less than half thickness, and was full of grooves. The rear brake was good for 30 yards; after that it faded and lost all power, and took at least 10 minutes to come back.
If the bike wasn't as worn, with everything from brakes to switchgear suffering abuse, I would have kept it and restored it, and fitted better quality suspension. I had a very fun year riding this machine, and will not rule out getting another one at some point, albeit in top condition.