No prior problems. Despite model year, I have not used it all that much, but over past 3 days, was running fine, but then started to run oddly: When running for a few minutes, it will start to waver consistenly between surges of power to down-powering when actively triggered for cutting. When this starts, and when idling, the motor races & the chain continues rotating. At times, when so fast idling, the moment I trigger for cutting, it powers down; sometimes even stalls. What is this problem/What do I do?