Setting too lean may well be part or all of the problem. Some years ago I killed a Husquvarna chain saw by leaning it out to max RPM. The upper ring fused itself to the side of the piston, knocking compression down because it couldn’t flex as the piston moved, and the cylinder wall got scarred up too. I learned later that the carb on that should be set by leaning it out until a certain RPM is reached and not to max RPM. It did really sing until it self-destructed. Fortunately on that model, the entire cylinder unscrews from the crankcase, and cylinders with piston , rings, and rod, are sold as a matched set, so the fix was relatively easy, but I won’t go into cost of parts!
Dave
