Like the Kawa Z200, the XS250 is a bit of a throwback to Honda's sixties designs, with a mere two valves per cylinder, single overhead cam and 180° crankshaft without any balance shafts, there's not really much difference between the basic design and any number of small Honda twins that were burning off much bigger bikes over twenty years ago. Unfortunately, the reputation for reliability and durability gained by those early Hondas is somewhat lacking in the Yamaha.
The XS knocked out 27hp but didn't have any low speed torque, needing to be screwed along at maximum revs to the detriment of engine longevity (as little as twelve grand).
Against hills, strong winds or when carrying a passenger, the bike could only move if screamed along in third or fourth gear lacking any point in the rev range where torque and power coincided to let the bike settle down into a relaxed gait.
Engine problems come from the carbs, crankshaft, valves and cylinder head. The carbs are difficult to keep in balance, give poor low speed running, are affected by rust from the petrol tank and don't work when pattern silencers or two into one exhausts are added.
The four bearing crankshaft is basically quite tough but does not survive neglect of oil changes, main bearings often needing replacement at twenty grand. Exhaust valves can burn out due to neglect and valve guides can fall out of the head.
The camshaft can become badly scored by twenty five grand and the bearings wear out quite soon after, but it's not as badly affected as the Honda CJ250. Engines that have been given lots of loving care and attention and not thrashed will last to around thirty grand when just about everything is worn out.
Handling when new was acceptable but nothing special. With a couple of years wear the shocks lost all their damping and the swinging arm bearings left enough free play to make Tiger Cub owners envious.
The bike was OK in town where the 375lbs could be flicked through traffic with relative ease, but bumpy country roads and worn suspension made it the least able of the Jap 250s. Even smooth motorways led to a mild weave above 70mph and only the very brave sped along at the top speed of 85mph.
Despite the need to scream the motor along at max revs, the XS returned 70mpg pretty much regardless of how it was treated. One of the advantages of a lack of balance shafts.
Vibration was never really a problem, although the motor was never as smooth as Suzuki's GSX, it was no worse than Honda's SuperDream. The motor could always be felt but didn't do any damage. Cycle parts were not of very high quality, with disappearing paintwork and peeling chrome after only a couple of years.
The exhausts disintegrate after just 18 months and have to be replaced with stock items. The chrome on the front forks becomes pitted, ruins the seals and loses the damping with fairly obvious consequences for directional stability. The engine casings quickly lose their shine and turn the cheapo alloy a dull shade of white.
Because most of the XS's problems are fairly obvious it's not such a bad buy as might at first be feared. Engines that have a quiet top end and don't make any obvious noises and have a good gearchange are probably going to be OK. Make sure that there's no low speed hesitation from the carbs.
Bikes that look good have probably been well looked after, it's one of those bikes where condition is reflected by the mileage and it's hard to tart a high mileage bike up. Bikes built between '78 and '80 are the most likely ones to be available for under £100.