ORIGINAL: TimBle
what Ken said.But i would add that the Yak has an enormous cowl with loads of drag so you may want to consider only props in the 12 and 13 inch range.Try;
11x6 (good starting point for small engines)
12x4
12x5
12x6
13x4
13x5
For my decathlon. anything bigger than 12 inch prop would cause dead sticks with my 55 AX. Not sure why, but eventually settled on the APC prop I mentioned earlier and have had no more dead sticks.