Small Engines (Lawn Mowers, etc.): full throttle, vent cap, needle valves

Question
I can't run my weed eater at full throttle. It always has to be chocked 1/4-1/2 way even when it has run for a while. I put fresh fuel with the right mix ratio cleaned the vent cap. Then after a while it will stall and I can't get it re-started until it cools down. There is no air filter to clean.It's like it is sucking too much air. Short of taking out the needle valves out and cleaning them and I'm not sure what the setting on them should be, I'm stumped. What am I missing.  

Answer
I would also replace the spark plug.  There should be an air filter in the trimmer...the only engines I know of that do not use filters are small boat engines and snowblowers.

As for the needle adjustments, they should both be turned out 1 1/4 turns from the gently seated position.  It sounds like it is running too lean, i.e. getting too much air.

Have you checked the engine compression?

Let me know.
Eric