loss of power to stihl fs80 petrol strimmer?

One your carburetor is out of adjustment or your High and low speed jets are plugged up. You need to adjust your jets and/or remove the carburetor and clean the jets. Most likely when you take it apart you will damage the gaskets because they will be stuck so you will need a rebuild kit. Check the setting of the jets. You will need a small screw driver. Around where the air cleaner is you will see 3 flat head screws looking at you. 2 of them are side by side and one will say "H" and the other will say "L". High and Low. Turn them clockwise BUT COUNT how many turn they go in. because you will need to turn them back out. What you are describing the Idle is to lean (the Low is turned in too far) and the High might be as well. You need to adjust your Low setting first. A good starting point on a clean carb. is about 1.5 turns out on both screws. This is a baseline setting. If it is clean it should start and stay running enough to get them set. If you have to turn the low out more than 3 turns then you need to clean the jets and rebuild.

David Trowbridge
October 2009