I just had a 3 hp Lightwin that had some binding in the gear case. I noticed it before ever trying to start it; however, I was just thinking that if one of your 3s had more mechanical binding somewhere than the other, it could result in no/bad idle, hard start and even lower compression with an electric drill. Just speculating that maybe you’re stronger than the drill, when pulling by hand, giving the slightly higher number? Dunno, just a thought.
Long live American manufacturing!