"Is there something that could have come loose inside the carb?"
I don"t think so. My Ford 8N and my "65 MF202 both have M.S. carbs on them. The main or high speed jet is threaded into the carb top, if I"m not mistaken. Can you see the body threads in the carb? How do the threads on the needle look? Spring in place, not that that should matter.
It"s been a while since I"ve had one of my carbs apart, but I"ve never run into this problem. I guess it would be possible for the brass needle threads to strip, or even the cast carb threads for that matter. Got me to thinking now...
Hopefully someone will come along shortly to help out, I"d like to know.