What no one has mentioned yet is that a 61 size engine is 3 engine sizes larger than 40. That means that unless you increase the fuel tank size to a 14-16 oz. you will have very short flight times. Most airframes built for 40-46 size engines won't accomodate fuel tanks that are this large. Even if you can do some mods and squeeze one in, now you will probably have double the amount of fuel in the plane than for the 40 size which also adds to your weight problem. []