For the record, Ys engines do run quite happily ion 20%. Infact, if I am not mistaken, japanese flyers can't use 30% nitro so the engines are designed with 20 something percent nitro in mind. I am not completely sure about this, maybe a japanese flyer could clear it up. Also, I ran a 140 for many years on 15% coolpower, it ran a treat. However, it was set up by a very competant YS guru.