My unit will idle but when you hit the throttle, it dies. Spark plug, fuel, lines and fuel filter are fine. Cleaned the air filter and the oil. It will start, but when I pull the trigger for acceleration it dies, no matter where I have the choke set. I did replace my upper shaft assembly a couple of months ago. Could this be a problem with the clutch? Does this model Ryobi have an automatic cutoff if the clutch does not engage?