OK, here's hoping this works :
This is in one of the featherweight user manuals pages 20 to 23
http://www.ismacs.net/singer_sewing_...ght-manual.pdf
page 20 and 21:
[ATTACH=CONFIG]426897[/ATTACH]
page 22 and 23:
[ATTACH=CONFIG]426898[/ATTACH]
I find typically that the spring hanging down to about 6 or 7 o'clock before it's put back on the machine works as a good starting point, then of course you coax it up over that rest that it usually sits on. That should give it pretty good rebound.