I have a ms361 stihl, bought new 6 years ago, it has cut about 20 cords. it has been well cared for, i use 89 octane and use stihl oil for mix. was cutting yesterday and it died sudden like , still had 1/3 tank of gas. does have spark, but won't even pop or run. lately it didn't idle down very quick, took 30 seconds or so . where do i start