Well, I went and took a look at it. It was in decent shape. It was also a dog. I tried to walk away, but the guy kept goin down in price. I finally got a somewhat lightly used cs-520 for $100 from a very nice old fella.
Here's what I have found so far:
It has a freakin 20" bar on it. Yeah, I thot that may be a bit much, then I looked at the bar and chain: It has 3/8s on it! It is a Windsor Speed tip bar and you can still see most the paint and some of the writing. So not only is it a 20" bar, but it isn't laminated, either. So, for a 50cc, this thing has a bit of weight. Easily a lb more than my 250. The chain is a full skip Oregon full chisel, brand new, 70 linker.
I cleaned it out, trimmed the tabs, removed the screen, and messed with the adjustments. It was insanely lean. And is it just me, or does the low adjustment on the 520 seriously affect the idle? I had to richen the L up a lot to get it to idle decently. I set it to 4 stroke on the top end pretty well. It does sound like about 13.5 mebbe 14. It is not limited - I had it screaming before I richened it up.
So, ok, I take it and the MS250 - both with sharp chains, to the fir wood pile. The 520 absolutely buried it. It pulls this 3/8 70 link chain through fir better than a bud's totally stock 346XP does it with a 325 chain. I need to make a video of this thing before it explodes. No camera until tomorrow, though. I'll have more video tomorrow. Me and sawfun9 will be cutting on some big Fir.
You didn't mention a muff modd which really wakes this series up. Steve