It sounds like it is time to tune the carburetor. This generic description of how to do it may be useful:
http://store.chainsawr.com/blogs/tu...ment-and-tuning-of-a-chainsaw-carburetorNote that trimmers like yours use chainsaw carburetors. Where it says you should start with the mixture screws 1 turn from all the way in, this depends on the brand of carburetor - in my experience one and a quarter turns is more common as the starting point. Before you start, however, measure the screw positions as they are now, so you can easily go back to your starting point where you at least know it will run. To do that, check where the screw slots are pointing, and gently rotate each screw clockwise until you feel it touch the seat lightly, keeping track of how far you have rotated it. Write down how far it was for each mixture screw. Then set them for your starting point and see if small adjustments make it better or worse. Hint: it is almost certain to end up within a quarter turn of one and a quarter turns out - but a quarter turn is a lot in terms of the effect it will have on how the saw runs. If you end up with it more than one and a half turns out, or less than one turn, the chances are you are doing it incorrectly, or the carburetor needs cleaning and perhaps new diaphragms or other parts. The diaphragms, in particular, tend to age, especially if it has been run on fuel containing ethanol.
