I sat down with my brother-in-law to work on our 1980s XLs. (He's got a 250 that needed the kill switch replaced.) I pulled the carb on mine so I could install my "fixed" air tube, and when we were putting it back, a small spring fell out.
At first I thought it was the spring for the choke hand lever, but it was too small, and that spring was still in place. After looking around a bit, I found that it was the spring that opens the choke valve. This means that when I turned off the choke, the valve wasn't opening.
Here's a pic of the spring back in its place:
I could tell there was a cap missing, and I found it on my garage floor. (I had found it earlier, but didn't know where it went, so I had put it in my toolkit.
I tapped the cap back in place, but I wonder if that will hold it. Should I do something to make sure it doesn't come loose in the future?