Why doncha get a few different props to experiment with...if that .61FX is still "healthy" (good compression, runs well ) I would try an 11 X 7 APC and a 10 X 8 and 10 X 9 just for the heck of it
The engines only about three months old so shes still healthy, Ive tried a 11/7 APC a12/5 and a 12/6 but get better speed from the 12/4 also I just switched too the coolpower I normaly run Byrun 15% cas/syn mix what fuel do you like? Watch the vid above and tell me if the engine sounds like shes turning where it should with a 12/4. I thought about drilling out the muffler wasent sure if it would hurt anything though, the first thing I did was remove the baffle. Im running a bit under proped becouse of the drag issue with it being on a boat.