My Yamaha dealer has warned me about mixing aviation gas to increase octane level. It's a 'dry' fuel that reportedly causes burnt valves and pistons. It also contains a bit of lead which is not recomended in Yamaha's service manual, which mentions it can cause serious damage to valves and rings... I'll use Klotz octane booster instead as it's supposed to be the best one. It raises octane 2-1/2 numbers per ounce, up to 10 numbers. So I'll try 1.5 ounce per gallon with 91 octane fuel =94.75 for about $0.25+ per gallon.