What is the value of a 1919 portable Singer sewing machine serial number G8137199?

This will depend on the age of the machine, the type or model and the shape that the machine is in. Most people asking this question are referring to the old tredel-type machines. Many were made, most are still around. When I had mine apprased the value was $300. Mine is in Excellent shape, still works great and has all the accessories.