HP numbers are worthless for comparing model plane engines ..I have converted a few 125s and one 100.Best rpm from a 125 was 8000 with a 16-8..Don't remember what the 100 did..
the bores are cast iron, and were not perfectly round and straight..I had the bores honed to just clean up and make them round and straight..the piston rings were a little weak, but when broken in seemed to work OK..The plastic block under the carb is easy to strip and probably not flat, causing loss of crankcase pulse, so take the carb off and lap the plastic on both sides..Take care not to tighten the screws too tight..Easy does it..
Be sure the carb diaphragms are not stiff, use an electric start, and they will run pretty good after some break in time...
John Maloney had a good idea there..With a little more attention to detail they would have been fine..The converted 100 was a good little engine..The ignition circuit fits inside the mount, with the heavy mag rotor and crank cut off..A G62 coil fits behind the cylinder where the source coil was, and makes a nice small package...Ball bearings on the crank and rollers on both ends of the rod...There is a small weed eater , John Deere brand, that had the same size bore and had a better piston ring..I used fixed timing, set at 28 BTDC..No syncro spark needed on such a small engine. Hand starts are easy with CD ignition...