I have a Stilhl fs90 that starts up fine, runs fine on idle but once the throttle is pulled it starts to sputter. Took it to repair shop and he put a new carb kit on it and cleaned out the muffler. Said compression was a little low, although the other mech thought it was good. Get home and try to use it and it's still doing the same thing. I'm stumped. Maybe a gas line issue? Any ideas?