I am in the process of switching from Echo oil to Schaeffer 2-cycle synthetic oil. I read on lawnsite all the time that you can go to 80:1. Where is the source of this recommendation? Anybody know if trimmer technical people have agreed with this? I am a little hesitant since I have been running 50:1 and the only problem is port and piston getting dirty. I am now into the 4-mix stuff and I don't want those valves getting dirty.