Small Engines (Lawn Mowers, etc.): craftsman weedeater, sears craftsman, exhaust ports

Question
I have a sears craftsman weedeater that I bought two years ago.  The problem is, it turns on but as soon as I push the gas trigger it turns off.  I put a new gas line, spark plug and clean the carburetor.  That happens all the time, it can stay on for awhile but as soon as I press the trigger it turns off.  What should I do next?  

Answer
Did you adjust the carb?  Was the fuel line rotted...is this why your replaced the fuel line?

Does it idle fine?  Have you cleaned the muffler exhaust ports?  Can you send me the model number?  The model number format will be something like xxx.xxxxx or xxx-xxxxxx.

Eric