These figures were obtained this past weekend when we tached a US 41 with an upgrade from RCign (straighten and true up hub) and the addition of a WA144 Walbro carb (same carb that is on a Quadra 52) Proped with an 18 X 10 Pro Zinger, the US 41 turned 7700 rpms static on the ground.
I've seen a U. S. engine so equipped power an American Eagle 85" span P-51 at 24 pounds and a Yellow Aircraft Spitfire, I don't know how much it weighed, very adequately. I was actually very pleasantly surprised at the level of performance obtained with this little engine upgraded as described above. One engine was running a straight header pipe while the other was using a B&B Muffler.
For the price, with the upgrade, they are hard to beat for reliability and performance in an engine that size.

A US 41 tached today turned a 22-8 Mejzlik 6000 rpm..
Same engine, 5 minutes later, same prop, with a WT76 carb,1/16 larger diameter, turned the same rpm..Some engines respond better than others..
22-8 at 6000 shows about 25 lbs thrusat on the ThrustHp chart
18-10 at 7700 rpm shows about 18 lbs thrust on the same chart..
A 22-10 Zinger shows 34 on the chart, 28 on a spring scale hooked to the tail wheel of a plane....