Google lead me here with a post similar to my problem...

But it does not describe the problem exactly. I have a Craftsman Weed Whacker (model escapes me) that was running fine yesterday morning. Mid morning it started racing, and I was having to choke the engine down to keep it running at a speed that seemed normal to me. By afternoon it would start and run for a few seconds up to maybe a minute, and then die. The gas I am using is about a month old. I burned through about 2 1/2 tanks before it started acting funny. I had used the the weed whacker previously with no problems, but it is not brand new. My father's new wife has had it for several years but had stopped using it because she was having trouble getting it started.

Here is a link that might be useful: The post that lead me here