Have an old white rotary machine # 151 or possibly #247

SOURCE: Singer Simple bottom thread is loose

hi there
raise pressure foot up thread making sure thread passes between thread guide this should solve problem never alter bobbin tension,
mary h

SOURCE: not sewing - jamming

Could it be that the feed dogs are down? I also have the 15358 and when I opened the bobbin area to clean it, I had this problem. Apparently, when you open the clips around the outside of the casing, it pushes the lever that adjusts the feed dogs to the right (lowering them). I didn't even realize it at first. Check your manual for adjusting this lever to raise the feed dogs. That might solve your problem.

SOURCE: Singer Sewing Machine model 9224. Bobbin thread

If you turn the handwheel, can you see a metal ring rotating around the outer edge of the bobbin case? If not rotating, broken gear or timing belt off.
If that ring is turning, remove the needle plate and bobbin case. As this ring now rotates, you will a finger on the ring that will pass behind the needle from right to left and it should catch the thread from the eye of the needle. If this finger, the "hook" passes above the eye, you have a timing problem.

Let me know.

SOURCE: I need a Domestic Rotary 151 manual. Any thoughts

I found a manual for Domestic rotary by googling Domestic rotary Manual - got a copy of an original old one - try: http://www.clawges.com/sewing/domestic_rotary/index.html