I've had the '83 Heritage Special in the warm winter workroom for the past week.
Got this pulsing in the front brake at very low speeds. ggGary's thread from 2010 was helpful in sorting it out:
http://www.xs650.com/threads/front-disk-brake-runout-heritage-special.1819/
I found that the runout in the disc was well over spec, and it was heavily grooved from a crumbling brake pad. The mating surface was running true.
I remembered that I had salvaged a rotor from the '78 I bought a few years ago for $100, and dug it out. Thankfully, it is in superb condition; minimal runout and wear.
Got new pads and checked the caliper in regards to the piston moving freely: AOK.
Next, replaced the clutch cable and surfaced the worm gear contact area on the side cover to remove that nasty casting ridge.
Replaced the pushrod bushing which was quite worn.
Replaced the chain with a new HT item, and bought new sprockets, dropping two teeth on 5T's suggestion. 17/32
Pulled the carbs and cleaned them, installing 135 mains (again, on 5T's recommendation), replacing the stock 132.5's. Drilled out the brass plugs hiding the idle mixture screws and adjusted them to 3 turns.
Following a cam chain and tappet adjustment, there was nothing left to do than to take it for a spin!
It was my unusually good fortune that it rained heavily friday night, clearing the streets of road salt, and when I woke up saturday morning it was 62 degrees at 8am! A freak warm spell for Syracuse NY. By 3 pm the streets had dried pretty well, so out it came.
The brakes feel great, the performance is excellent, idles good, although I need to do a bit more work on the clutch.
Back in the winter workshop, I slapped into the AIWA a favorite old cassette recording of Bob Marley live.
...and pulled in the next winter project, the '73 DT3 250.
Couldn't be happier