So after a little more research and riding, I have determined a few things:
1) the bike does seem to work fine. Rode it in the city then took it for an hour ride on the highway to make sure it does everything well enough.
2) It is kind of slow to warm up. I started it with the choke pulled and had to keep it pulled for a bit in order for the bike not to die.
3) Once the bike was warm, it seemed to be idling too fast. There's no tach obviously and this is not a bike I'm used to, but in my experience the idle seemed to be pretty fast.
4) The owner said if it stalls, it backfires pretty good when you start it back up. Wasn't sure what to make of that. I mean backfires happen and I didn't experience this, but the fact that he said something made me a little wary.
5) I need forward controls and/or highway pegs. Are there affordable ones for this bike? I'm having a lot of trouble finding info on the '91 1500. What parts for other years are compatible with this bike?
Items 2-4 seem to be due to the bike being running too lean. The idle is probably set fast to keep the bike from stalling when goosing the throttle at standing starts. The bike taking too long to warm up is more a fuel starvation issue, as far as I can tell. Backfiring is also a lean condition.
When was the fuel filter last changed?
04 1500 Classic
Sissy bar, luggage rack,
light bar, 2" risers,
Isogrips, Fatbar crashbars,
offset hiway pegs, tank bib,
new brake pedal, throttle lock,
Cobra Lowboy Shotgun pipes,
Baron's Big Air relocated right side,
tombstone tail light,forkbag,
detachable hard leather bags,
alarm, power port, clock,
and a cool cupholder