99-13 Not Picking Up (curved-top) Bobbin thread?

Hello!
I own a Singer 99-13 from the AC prefix, August 29, 1929 run. The machine has sewn for me before. I never adjusted anything since when it was gifted to us. Then I cleaned the bobbin case from any duff, exchanged a re-pop (non Singer) needle for a Singer mid-weight cloth needle, and hand-turned the wheel to create the first bobbin-thread loop with the needle thread, then pulled the bobbin thread up from that loop - and placed the needle thread and bobbin-trailing thread under the presser foot, where both thread ends trailed behind the presser foot. Like regular... sound good so far?
Then I place two pieces of 4" cloth squares under the foot, and lowered the foot. I hand-turned a couple of needle cycles to get things started, and leaned into the operating lever and commenced sewing. The needle thread was breaking before, but I tightened the thread discs (tightening/loosening) knob (for 99-13, not the later dial) until there were almost three threads showing on the stem. I could feel no slight tension when pulling the needle thread from the spool, through the threading points, but "3-threads showing" was about where the spring-friction discs was set at before I got my mitts on it.
So, does anyone have an opinion on why by bobbin thread isn't being picked up by the looping mechanism (that hidden within the cast frame)? The needle thread seems to be staying intact. I looks almost sewn on top, except for the missing bobbin thread. Thanks!