I wrote to stihl about my 4 mix product and got a call the next day. I learned some valuble information on the 4 mix engine. The guy told me to run only synthetic stihl 2 cycle oil and run it a littler leaner than rich. I've been using echo power blend and was told that's a no no. Maybe some of you on here that have had bad experiences with the 4 mix might have been using bad oil and gas which greatly affect the engine. How have everyone's 4 mix engines been running?