It's definately too small. 10.500 on the ground slobbering rich is not good but since it didn't want to run right with the 13x11 I had no choice as I had no other prop. I'll use the 12x11 for break-in, running it rich so it doesn't go above 11K rpms and then I'll try the 13x11 again. If it's still to big I'll try 13x9, 13x10 etc. I'll definately go up an inch in diameter to decrease rpm, noise and all out speed, in exchange for better vertical performance.