Old Suntour X-Press Accushift thumb shifters (7sp) and Suntour X-1 rear derailleur (7sp), Suntour 7sp freewheel, on an old Trek 930.
Bought this bike cheap at a garage sale, trying to get it working. I believe the above parts are all originals.
Problem: Shifting from smaller to larger cogs on the rear wheel works great, but going the other direction doesn't. The derailleur doesn't move quite far enough, so the chain just kind of rides in between cogs, and doesn't make the full jump to the smaller one. If I twist out the barrel adjuster any more, then the jumps from smaller to larger cogs are too big, and the chain starts to rub against the next highest cog.
(Chain definitely needs to be replaced, but I haven't done that yet. I don't see how that could be the problem, though.)