The mainspring on a Royal standard of this era with a regular sized carriage should be set at between 1.25 to 1.5 pounds, or sufficient to move the carriage to the extreme left.  If your issue is the "carriage is not reacting to the pressing of the keys", even at the begging of the line, but you know there is tension on the mainspring, your issue is likely related to something else. You can simulate the tension by pressing on the right side of the carriage while you press the keys; if it is still not tripping, you have a different issue.