Ido run YS and other then getting them to idle easier and my pocket $10.00 bucks lighter Ihaven't seen any difference between the 15% or 20%. When I tried 30% I noticed how much quicker my pockets got $20.00 bucks lighter!! Ididn't notice much difference using the 10% either, 5% took a lot of work getting the idles set but it does work. The 15% just seems to be a happy middle and it's always around.