Well, I have stihl blower less than two years old and it done the same thing...Come to find out that the muffler screen was plugged not letting any exhaust gasses out.... Look at the muffler and unscrew the bolt looking thing with the hole in it. When you get it out you will see a screen attached to it that come out when you unscrewed it from the muffler... Take torch and Burn the carbon off the screen so exhaust gases will now flow out the little hole... May not your problem but I would make sure it not that for I would do anything else????

When it is idling the clutch is dis engaged, When you hit the trigger to speed up the clutch engages.Maybe the trimmer head is jammed up.
Kind of like trying to drive a car in front of a brick wall.

Could be clogged muffler, and could be tight trimmer head, but my money is on gummed carburetor. You probably need to disassemble, soak the carburetor, and install a kit, or replace the carburetor. Also suggest replace fuel lines, if they aren't already so hard that they break when you remove carburetor.

I'm with ggoyeneche-

I have a Stihl FS55 trimmer that had the EXACT same symptoms last year. I believe due to the Welch plug coming loose inside the carb.

Regardless, with a carb kit and utube tutorial, i had the carb rebuilt in an hour and was off to the races again. Carb kit is cheap and I bet you a donut it'll fix your problem.

Be sure to take your carb off the trimmer and take it with you to the Stihl dealer. They use different carbs and the make / model / serial #s are important to make sure you get the right kit.

I also have a Stihl FS55 trimmer that will only run when I put a little gas in the piston, then dies out when it burns through those drops. Replaced the carb, fuel filter and spark plug with same result. Took it to the dealer and am told it is a bad coil. If it was a bad coil i would have to believe it wouldn't start at all. Any thoughts? Thanks

Appreciate the follow up. I cannot get it to fire unless i pull the spark plug and drop some gas in the cylinder. Then when that burns off it will not start or run, it just dies out.

Sounds like fuel starvation , which normally includes everything you say that you have recently replaced. Ensure you have fresh fuel and add 2 ounces of carb cleaner let sit overnight. Choke , prime the unit and attempt to restart the unit again. if this fails remove the jets and clean with spray carb cleaner . Reassemble and initiate normal starting procedure. It should attempt to start , if not prime unit via the spark plug , continue to alternate starting proceedures until unit fires and run the unit at mid range. You may indeed have a faulty coil , however fuel starvation is your 1st problem . Once the unit runs continously for at least 5 minutes you can rule out a defective coil. Let us know how it goes !

why does my primer bulb go dry while running the weedeater / then dies

The fuel line from the primer to fuel tank is obstructed .There are two lines on the primer suction & impulse to carb .

I’ve got an FS85, that revs nice and high when it’s first started in the start mode but as soon as I pull the trigger and click it into normal run mode then I can no longer rev it high without bogging down and stalling. I cleaned the carburetor, clean the spark arrester and no improvement. Thinking maybe the whole muffler is clogged, I took the muffler off completely and ran it that way and it does the same thing. Could it be something going on with the start switch trigger that when it kicks into run mode it has a bad connection to the coil?

Would a Stihl FS 55 work if the primer bulb is broken?

Everytime I have had the primer bulb crack/tear, it leads to the weed eater not running correctly (if at all). Others may have a different experience and opinion, however.

Also, the Primer bulb is an easy fix. If you have another one either new or used in good condition, you can swap them out in 5 minutes. Idk if this helps, but hopefully it'll be of some benefit to you or someone else.👍

Purchased a brand new brushcutter and does the same thing. perfect idle and start but rec it andbit wants to stall. frust frustrating

If primer bulb and fuel lines ok, then either carb gunked up or in need of new diaphragm or both.

For those with the FS series (in my case the 85) i also had issues when pressing the throttle / bogging down - stalling. I reset the carb adjustments as per the manual... problem persisted. I did notice however that the head was spinning slightly...so i turned the (LA) screw counterclockwise 1/2 - 1 turn at a time, periodically testing throttle. Eventually i found a sweet spot wherby the throttle when pressed fully no longer bogged the engine and was super responsive. Thanks