[Oberon]

On the other hand there is a huge market opening up for a Gasoline additive especially formulated to keep these small engines running properly for use with E15 Gasoline.

Avgas is the answer. 100LL will keep your mower happy. Good thing you never need more than a few gallons at a time...

[Clay Moore]

Maybe in the higher compression overhead valve engines. The last time I tried it in the old L-head Briggs, the lead deposits built up to the point that the valves would not shut.

LL stands for “Lots-o-lead.” (^;