My father-in-law gave me his Echo pole pruner. It was sitting in his garage unused for a few years with stale gas in it. I drained the old gas and put fresh 89 octane and Echo 2 cycle oil in. It starts up easy and will run fine with the throttle, but if I let go of the throttle, it stops. Did the old gas gum up the carb, and if so, is there an easy fix? Thanks!