I have a stihl pro trimmer. It starts fine on the first pull. It idles well, but when I squeeze the trigger to speed it up and use it, the trimmer dies.
what might my problem be?
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.