Due to the newer carb standards their is no universal rpm or settings for a weedeater you would have to contact a service center to look up the settings for your weedeater, they also normally take a special tool nowdays that you would have to have to adjust it.
You need a"Pac Man" carb adjustment tool.
get a stihl
The carburetor on a Weed Eater Featherlite SST25 is adjusted by turning the screws on the side of the carburetor. They control the idle mixture and idle speed of the engine.
by turning the screws on the side of the carburetor
50:1. Be sure to use 2-stroke oil.
2.6 ounces of oil per gallon of gas. A 50 to 1 ratio.
Bad\dirty carburetor or not getting gas.
Change the spark plug and spark plug wire. Change the fuel filter. Change the air filter. Change the motor oil.
The owner's manual i have did not specify. You have to pour and check the oil until it reaches an appropriate level.
The exhaust could be plugged with carbon, carburetor has debris in it and needs to be cleaned, fouled spark plug
Check the muffler for obstructions. Dirt dobbers and other insects love to make nest in the outlet holes.
Throttle cable is probably pinched somewhere, or check the butterfly on carburetor, might have a broken return spring, or debris binding the shaft.