Just for grins, try an APC 10.5x4.5 prop. Launch at 10,400-10,600 rpm. Engine will hold that RPM in a solid 4 cycle and may get better gas mileage. I and another local stunt flier have tried about every combination of prop and fuel w/B-40s and find they do well running faster in a 4 cycle. Have found the TT prop loads them down too much. When broken in, (mileage improves with age) 4 ounces should do it but I still stay with 4.5 ounce tanks on B-40 planes...prefer 5 ounces for LA-46 and Aero Tigers but that's for another post.