Just checked a couple of the manuals I've got, it looks like the old 340 (mid-90s) had the silver/gold spring you had in, but the microfiche for an EDGE 340 says 110-290 – doesn't give a color and doesn't match up with the springs listed in the manual I use. Looks closest to either the blue (120-300) or gold (100-275), but the dark blue/white is pretty close too.
If you can check peak RPM, that'll tell you what you need to know (I know a lot of these don't come with a tach). If peak RPM is off, then you'd definitely help yourself out getting it where it's supposed to be, especially with a 340. If you're going by ear, it's pretty hard to tell. I've heard of people who thought their engagement was sky-high, only to put a tach on and find it was in spec. I think that's partly an air-cooled thing, they make more noise idling and part throttle.