Hi. I just got another bike, semi-new Schwinn, apparently hardly used for years.
I spent some time this morning making little adjustments and short trial runs.
I found that, when in the two highest rear gears, the chain would seem to bunch and lurch.
Of course, I couldn't see perfectly what was going on.
The teeth are fine on the gears,
so I thought maybe the derailleur wasn't picking up all the slack in the chain.
I adjusted it out all the way, trying to make it tighter.
It seemed to help a little for the 2nd-highest gear, but I may have been imagining it.
So, for now, I just adjusted the tracking max to not allow it into the highest gear.

The chain doesn't seem to spring much on the jockey wheels,
but I've gotten used to using a fairly short chain on my Peugot, so I'm not sure.

Does anybody have an idea of what might actually be going on?