Good info Gil ... thanks for posting that. I wonder if my old stale Coleman fuel also has a bit less punch?
I will add the caveat that you need to be careful not to overstretch your springs like I did. I stretched a little and didn't see any change, so stretched a little more and still didn't see any change, then stretched a little more and all of a sudden my throwout weights would no longer pull in against the hub, so the engine would barely run if at all. You can't really re-compress this type of coil spring effectively, so I made arches of them which were held in place with the clamping action of their mounting screws, thus making them somewhat adjustable by varying the amount of arch present. I'll try to post a photo to show what I'm talking about this pm.