RE: O.S. 1.08 prop
A 14 x 9 3-blade propeller would actually be much more load on the engine than the 15 x 8 prop you were using. You may need to go smaller, like a 14 x 7 or 8 3-blade, or even a 13 x 8 3-blade. You want the engine turning the same RPM as before, and then you need to adjust for how the airplane performs.