in my buggies (completely different engine) i run 9% synthetic & 3% castor. for marine i was wondering if i should keep the ratio of castor to synthetic roughly the same as buggies (ie 14% synthetic, 4% castor) or go 50:50 as in lots of shop bought fuels. i intend on using Klotz synthetic oil and castor in my OS outboard. any suggestion would be appreciated. from your post topfuel, i'm guessing a 15% 3% or 14% 4% synthetic, castor respectively would be a good starting point.