The simple answer is that a given weight fly rod is designated that weight because someone at the factory thinks it cast best with that weight line. That doesn't mean that you're necessarily doing anything wrong if you want to use a different weight line on that rod.
That being said, it is also true that a semi-gorilla caster like my self could easily break a 2 weight rod with no more than 20 feet of 6 weight fly line outside the tip. When you know the given line weight of a rod, its best to stay within one line weight of what the mfg says.
I'm 95% sure that those rods you found are somewhere between a 4 and a 9 wt, but that's all i can tell you, except that if its the size of a chapstick tube near the handle, it's no four weight. I you can tell me where you are, I can get you to a shop that would have test lines to try on those rods.
You might have gotten sweetheart rods for a steal, or maybe just a whip. If its a Fenwick, we just might all be jealous.