RE: Biggest engine for a U-Can-Do 40 size?
Your 65LA weights 23.8 oz with muffler . Put a 13x4 or 13x5 prop on it and have fun . I have a Magnum .91 four stroke on mine now that weights about the same and the plane flies good . I have thought about putting my Saito .72 on it just to see how much difference there is .
Barry