My weedeater want start change spark plug - Poulan WeedEater Hedge Trimmer 25cc Engine

Try a new spark plug. A bad spark plug will spark in the open but not under compression.

You need to be sure you're getting fuel and spark before you do anything else.

Ok, so you have fuel, do you have spark?

remove the spark plug , an go in dark area, pull start , do you see sparks , or just grab the plug an pull it, does it hurt.(ground one side of hand to the metal so it don't course thorough ur body.
so you have spark or not ,
no ,then theres the answer magneto is shot.
yes, then take off the filter an give it some gass or just spray a bit in cyl as you put the plug back from testing the spark.
does it cough or run when gas is added into some port
no then the cyl is cracked or needs oiled , spray some oil an gas in the head w/spark removed, let it set .

Were any of the cooling fins damaged? This is a totally air cooled unit, air flow and fins are required to keep the unit cool. Make sure the fins on the cylinder and head are clean, the blades on the coil are clean, also check the spark plug to make sure it is the recommended plug, is the muffler clear? check airfliter and always use pre-packaged fuels.
Only other cause would be the carb has been set to lean, but I doubt that.

If there is no spark then I would suggest checking out the plug wire for cracks or breaks If there is none present then the ignition coil could be finished Take it off take it into your small engines dealer and get him to test it.

possibly on/off switch-has it gotten wet? Also check where wiring from on/off switch meets the wiring from the weedeater body.Check those connectors/crimps make sure theyre plugged in /right fit and not wet.Make sure youre ground wire is grounded/attatched/screwed to the machine.Ive had a weedeater get wet twice at the on/off switch and had to bring it in the A.C. overnight to really dry out.It worked.Hope this helps.If none of this does then its maybe the coil(semi-internal-no fun) or the fat wire carrying the spark from the plug to the body(semi-internal-no fun).Good luck!

take the spark plug out and pull the engine over with the spark plug in the wire and ground the plug to the trimmer and see if it sparks. if not flip the switch the other way and see if it sparks then you shall know.

Are you using mixed gas? The gas needs to be mixed 50:1
You will have to use 2 cycle oil. If you are using mixed gas, than you can buy a cooler spark plug.
Sounds like the spark plug is not properly gapped.

Stihl weedeater was running and stopped suddenly. Put in a new fuel filter and cleaner air filter with soap and water. Checked spark plug and it appeared fine. Started the weedeater, ran for a second or so and stopped. Spark plug wasn't gas fouled. Could it be the carburetor needing new diaphram gasket and spring.