This is a Poulan Pro Link model PPB 250E week

You may go to the following link
https://www.partstree.com/parts/poulan/hedge-trimmers/pp2822-966513101-poulan-pro-hedge-trimmer-2011-03/engine/
for an exploded view of the equipment which may help

My chainsaw was doing this.The carburetors on these small engines have a fuel inlet screen that clogs with tiny bits of debris.Remove the carb,and take the portion off that has the fuel line attached to it(if you're careful,you can reassemble it without needing a new gasket).The screen is about 5/16" in diameter.Spray some carb cleaner in there to clean the screen out.(this is mt best guess,because it sounds like a fuel starvation problem)

Your string head is part number 26 in the diagram. Home Depot's Garden department has a wide variety of parts including universal string heads and heads for Homelite, Ryobi, etc. and possibly one that will fit your machine. A lot of these trimmers have Poulan engine and trimmer head parts. See if you can get the complete assembly off the trimmer (if you haven't already) and take it with you to the HD and match it with a new one. The price of parts from an online supplier plus shipping will be almost as much as a complete replacement head. If you shop Ebay, there are literally hundreds and hundreds of weed trimmer parts on there and some good deals to boot.

http://www.mowerpartsweb.com/MANUALS/POULAN/PPB335.PDF

The proper way to test it is with an ohm meter by doing a continuity test. If your switch isn't working on the machine, there is the possibility that the wire from it that connects to the coil module is loose or is off. I would check for that first and then do the continuity test if needed. The coil is under the front cover of the machine and will require disassembly to access where the black switch wire spade terminal is.

1 1/4 turns out. Then let it warm up and adjust 1/8 turn lean, which is in, to make it run best. But that is only right if you just rebuilt it and everything inside clean and wrkn right. May have to adj in less?

Go to the Poulan web page http://www.poulanpro.com/node6556.aspx and enter the model number of the string trimmer. If the trimmer is a Weed Eater brand (owned by Poulan) then go to this page http://www.weedeater.com/node6507.aspx. I think you can also locate older model manuals in their archives.

HOW IS YOUR FUEL LINES. SOUNDS LIKE IT MAY HAVE A AIR LEAK

poulan ppb 330 33cc trimmer .idles but no high speed power.
my solution was to remove postage size screen on muffler known as spark arrester and clean. runs great know !

After all the bolts have been removed from the head, tap all the way around,(http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=4760615&PMT4NO=65151144), where the head meets the bottom of the motor. It will come off with a little coaxing.

Jim