How are you Phil? I saw your post about the little US 41 here and see that you gave the right advise. It will fly a 25 pound warbird very well with the modifications you suggested. I believe the carb is a WA 144 Walbro (available at B&B Specialties) My suggestion, if you do not have a noise problem at your field, would be to make a header pipe out of a flat piece of copper and a copper 3/4"elbow for the exhaust. The correct prop is very important on this engine and we have been using a 19x10 carbon fiber prop cut down to 18" diameter. Mine turns this prop at 7800 rpm. That will get your 25 pound warbird up and moving.