Should you consider buying a replacement engine, new or used, please consider the Thunder Tiger GP-42. It is more powerful than the O.S. 46LA, user friendly and less expensive. Remember, if you buy it new, that it REQUIRES break-in. Your idle and top speed will both be affected. Be patient for a couple of hours and you'll be rewarded! I have two of them, both of them behaved the same way, both are a pleasure to use...
Beppe