I have a Troy-bilt TB90BC weed eater/trimmer. It was given to me by a friend that I worked a side job for. I got the thing running and it will run strong but only for about 20 to 45 seconds each time. I can not keep it running solidly. Can anyone tell me what it is that I may need to do to fix this problem.

Remove and clean carb , install carb kit.
Check exhaust screen.
Luck