The later ('80+) bikes have a factory solid-state ignition system (its called a
TCI for
transistor controlled ignition, I believe) while the earlier bikes have conventional Kettering breaker points. There isn't anything wrong with the points, but they do require a little care and feeding and the mechanical advance units can be a bit troublesome if everything isn't well adjusted and lubricated. The TCI unit on the later bikes is basically maintenance-free, as far as I know.
I guess one difference is that if the breaker point system dies, it usually happens gradually and so you have some warning and can usually limp home if you know some tricks. On the other hand, in my experience with solid state stuff, it either works - or it does not and if not,
you are walkin'. Fortunately, the failure rates on solid state components is very low and if they are going to die, it is usually in the first few minutes/hours of service (in engineering we call that "
infant mortality"), so anything that is 35+ years old - is quite likely to make it 36+ years old.
The alternators are basically the same, with a minor (but important) change to the rotor brush connections in the 1980 and later bikes.
The bike's stock charging system is solid and consists of the alternator inside the LH engine case, a voltage regulator under the LH sidecover and a separate rectifier pack mounted directly
UNDER the battery (hardly the ideal location for a delicate electrical component, I'd say....
).
If everything is nice and clean and the alternator brushes are longer than 7mm, all is well, but the system does require some maintenance (largely the alternator brushes - which are a quick, easy and cheap job to change -
IF you have the proper JIS screwdriver). Many people opt for a solid state regulator/rectifier combo unit because they are reliable and inexpensive while the old electromechanical voltage regulator and separate rectifier pack may be pretty corroded and crusty on an old bike that spent a long time being neglected (my regulator and rectifier were both a total mess on my 1976 Standard). There is an aftermarket permanent magnet (PMA) alternator available that eliminates the brushes - but many folks feel that it is of poor quality. Fortunately, the stock alternator stator is rebuildable for not too much cash and so you should be able to keep the stock system alive forever.
Otherwise, the major changes of which I am aware are:
- the electric starter was introduced in (I think) 1972 and then revised in 1973 to eliminate the compression release mechanism on the LH exhaust valve;
- the fork tube diameter (34mm to 35mm in 1977);
- the front brake went from drum to disc in about 1972 and then the type of hydraulic caliper changed in 1977;
- the brake caliper position (ahead of the fork slider to behind it in 1976);
- the rims went from aluminium to steel in about 1979 (I think);
- and the styling (the XS Specials were introduced in 1979) and were the only model available after that single 1979 year in which both Standards and Specials were sold;
- the Specials have a smaller tank and some had cast wheels and the possibility of a rear disc brake plus after 1979, they had plastic sidecovers and more chrome.
As you say, the XS Special
in stock condition may not be the best for handling or comfort - but many folks change the bars and seat and wind up with a really nice bike. Frankly, I don't consider the differences year-to-year all that profound. All of the engines work about the same and I doubt that many people could detect the differences in the front brakes (after the switch to discs) - but the handling of a Special really is quite different with its smaller & wider rear wheel and wider handlebars.
I'm sure there are some other differences - but as stated above, Skull's excellent article details them very thoroughly.
