I've got Stihl problems. I have an old FS 80 trimmer, that when it gets hot - it wont take the gas, it just bogs and cuts off. My new FS85 is starting to do the same! It's not as bad as the FS80, I can still use it. The FS80, has had the following done to it so far... New plug, Muffler cleaned out, air cleaner cleaned, gas changed, fuel filter cleaned, carb kit installed, firing checked, new fuel lines installed. I run Amsoil 80 to one..(1/2 bottle to 2.5 gallons of gas) Next, I'm gonna try some stihl oil, just to see if the new one will straighten out before it dies too! Anyone have any ideas??