It happened to me last week. A friend brought over his Case 444 with a K321 running terrible. I pulled the carb and did a thorough cleaning. Put it back together turned the idle and high speed jets down to their seats and then I was interrupted before I could set them to their initial settings. An hour later went to start it and it just cranked???????
Fortunately only took me a minute or two to remember that I had not set them up. All was well after that.