I think may found the problem the ones used on the Echo trimmers here with the adjustable main mixture screw but I haven't got to try checking it yet as I got get in problem carburetor. In the following image you the tip has a cross hole. Well through the center of narrower tip is hole connecting the cross hole to the tip. I am think that hole is getting clogged. In order to get this needle out you got to remove EPA plug (cup) retainer.
[Linked Image from i.imgur.com]