As the owner of a small engine repair shop with over 25 years experience, I will tell you not to use fuel additives. We have been mandated 10% ethanol fuel where I live and work. Another few years and maybe 15% and I will be retired in the bahamas with all the money made from fuel system repairs. Yep, ethanol is the greatest thing to happen to me.
(I use startron-but what do i know?)