I just realized my Echo trimmer manual and blower manual say to use mid-grade gasoline, or higher, 89 Octane (R+M)/2. I have always been buying regular grade, 87 octane fuel, for all my small engines, and have been using this in my trimmer for a couple of years now, and have been using it for a few days now, in my new blower. I haven't heard any knocking or pinging. Not sure why I didn't read the gasoline requirement section of the owners manual before buying gasoline. I guess I just assumed all small engines are low-compression, and run fine on regular gasoline. My tecumseh engine -- the manual says NOT to use anything higher than regular grade, as it may damage the engine. Hmmm. I have 5 gallons of regular gasoline. I don't want to throw it out and buy mid-grade. That is nearly $15 worth of gas! Every other manual for every similar small engine, seems to say use regular grade. Why does Echo say use mid-grade?