What is this??
 

My Weed Wacker started running a little rough, then shut down completely. When I went to check the gas, a saw the little (1.5 inch long) cylinder-like thing sloshing around inside the tank (there was plenty of gas). The two photos show the thing and the gas tank opening. Anyone have any idea what it is/does? I'm guessing it must have something to do with the rough running, but the Wacker started right up after I removed it,....but then ran rough/weak before shutting off again. :(

Any information would be greatly appreciated. :)

Aha....fuel filter!
 

OK, with the help of Google/YouTube I answered my own question: It looks like a fuel filter that came off. Probably need a new one, but will try reinserting/reinstalling this one first. :)

That device also acts as a weight on the end of the fuel line so when the fuel gets low, the fuel line will always follow the fuel no matter what angle you hold the machine at.
Also, as the fuel line gets old, it gets brittle and cracks with age, which is what appears to have happened there so you should probably replace it.
Ask me how I know!

What they said. I had to get a new gas tank for my chain saw because there was just no way to get inside to replace that entire hose and filter. At least no way that didn't make me want to throw it out the window.

Same thing just happened to my 12 year old Redmax blower...wouldn’t start and all the fuel had leaked out onto the garage floor (heat wave and very warm garage) I’m thinking made the fuel expand and leak out.
I pulled a few inches out and cut off the broken part of the fuel tube then re-inserted it into the tank the pushed the tube back onto the carb. Started right up!

Thanks to those who responded to this. I've figured out that as long as I have a LOT of gas in that little tank, it keeps flowing and the wacker keeps wacking. Makes sense that the filter would also provide weight to stay below the "surface" (thanks Denis D). And yes, my fuel line is pretty crumbly, at least near the end. I probably should have kept it full all winter, rather than let it dry out.

You did the right thing by not having fuel in the tank. The ethanol fuel today has been a real problem for small engines and it is recommended either to buy non ethanol premix in a can and/or run it out every time.

Eh, I keep my 3 chainsaws, trimmer, leaf blower all filled with fuel and haven't had an issue. I do run them once every month or so to keep fuel flowing.

Problem I've had in the past when emptying fuel systems for long term storage is the diaphragms in the carb tend to harden. Fuel vapors can also expand and stretch plastic tanks if the fuel cap isn't cracked loose.

The fuel line breakage pictured here is more likely due to age and nothing more.