My Troy Bilt TB20CS weedeater will run for approx 30 seconds, then shuts off. Took it apart looking for a clogged screen/filter. No luck.

Any suggestions.

Hi,
Thought about it before answering because 30 seconds is a rare symptom. Sounds to me as if something is resticting fuel flow enough that the pump side of the carb cannot keep up. Two things come to mind and they are very different from each other but will yield roughly the same result. First grip the airbox (the thing the carb is contained in) and try twisting to see if it moves (rotates.) If it does, you have a weak air leak that keeps the pump from working strongly. The second would be a partially clogged fuel filter not allowing enough fuel flow.
Peace,
Clarke