Hey Edgeguy,My new YS is going in my Aeroworks Edge 540 60/90. Something strange happened today during runup. It's the first time I tried to lean it for maximum R.P.M.s. After two tanks of Coolpower 15% Heli I began to lean the engine.My tach(Glowbee Intellitach) gave me a 9800 r.p.m. reading.I leaned it some more and got a reading of 10,500 r.p.m.s. I was in shock and continued to lean some more and finally stopped leaning at 12,000 r.p.m.s. I immediatly opened the needle to richen just in case these readings were true. This was with an APC 15/8 prop. I suspected a faulty tach, so I went in my garage and opened a brand new tach of the same brand,put a new battery in it and tried to repeat the process. Sure enough I got the same readings!! This can't be or can it. I was so shocked I packed up my gear and drove to my LHS and discussed this with THE local engine guy who is very familiar with YS engines and he said you probably are mistaken on the 15/8 and was more likely a 15/6. So back home I go and upon checking the prop I discovered it is a 15/8. Tomorrow I will try a 16/8 APC and take readings unless the Hurricane has other ideas. What do you think of this??