Got a new 5600 last year.. Has always been a little quirky about idle speed changing whenmoving the saw around\changing positions, also came pig rich out of the box. It has also always "burped" some when running with with in the cut even when tuned to 13000rpm... An odd occasional brrrp with a deeper tone. Now the saw surges when reving under no load and didn't want to rev past about 12200 no matter what. Anyone have any thoughts? Should have probably exchanged it last season as I never felt like it ran quite right. Hasn't been abused... 50:1 on saber or stihl always