HercDoc,

Be sure to consider how this plane should be flown. You cannot overspeed the FuntanaS airframe or you will face catastrophic failure. This plane MUST be flown slow. You want low RPM torque and instant throttle reponse for this plane. I would go with a 4-stroke...and I did. I have a Saito 180 on the front of mine. Now, this is way more power than needed but I had the engine and couldn't spend another $300 for a new one. I am very happy with it thus far. If I were to buy a new engine for this plane I would go with the YS 110, although the Saito 120 will fly it nicely. Good luck!