My stihl fs90r 4 mix has been running a little weird for the last week or so i know its not the carb or anything it runs great at WOT but when i walk from one area to the other it sometimes dies. Also it has been a little harder than normal to start and a couple times i have pulled on it and it has compression and then i cant get it to go any more i have to let the string recoil and give it a good jerk. This trimmer is just now one full season old i would guess 300-400 hours of operation. Does anyone think that the valves need to be adjusted? Any other ideas what could be going on here?