I have a Yard King 39" riding lawn mower (Model #C3913000; Code 2052; Serial #S001010322644). I need an owner's manual desperately! Any clues!!

Hi,
It will be next to impossible to find as that is a Noma, bought by Murray, since bankrupt, taken over by Briggs & Straton, factories closed and product outsourced to AYP. Many hard feelings existed and most parts breakdowns and manuals "disappeared."
Find a very long time dealer to try to find some info is the best I can tell you. The best I can find is a reference to one page; I can guarantee it will be nothing but the parts that are all not available. I am afraid it is a common story in most of the story of Noma.
Peace,
Clarke