Puddler

I do not think you will find a weedwacker engine that has any ware near the power the US41 had in it. Most weedwacker engines are 32cc or smaller. With Homelite and Ryobi being the most popular. These engines put out a lot of thrust for their size, but do not put out the power as compared to a US41. If you want something that comes close to the US41 you will need to use a chainsaw engine like the homilte 33cc or 45cc. The 45 will have almost the same power as the US41, but will be heavier. You can put on a CH ignition and the weight of the engine will than be about the same. This does cost more and after you buy the CH ignition and the conversion parts you might as well have just bought another US41.

What type and size of plane is it you have. Maybe one of the weekwacker engines will do. I believe the Ryobi 31cc is the easiest to convert, but the homelite 25cc has better power. I fly a Ryobi 31cc on a Balsa USA stingray 120 thay weigh's in just under 14 lbs and she flies great. The plane has an 83" wing span with 1276 sq. in wing aera. If your plane seems to be this size or close to it either the Ryobi or homelite should fly it just fine.

Good luck