I have 3 Stihl KM 90s. They are the same engine as the FS 90 trimmer. This problem has happened to the 2 older ones. Gas leaks into the air filter when not in use, no matter which way trimmer is positioned. I ordered a new carb and its still happening. Could it be the gas tank vent? Is there a way to clean them or do I just have to buy a new one. Anyone have this happen to them. Its starts and runs just fine without a gas soaked air filter on it.