Did it by any chance back-fire on you lately, like on or around the time of the power loss. As said in an earlier post I had a new magnum .91 backfire. The result being power loss(RPM) and eventually a broken connecting rod at the crank journal. You may want to pull the back plate off and check for an egg shaped connecting rod end, if you didn't figure it out yet. I was swinging a 14-6 prop almost 9800 before the back-fire and after only 7500.