All cylinders had compression checked 125 lb up to a hundred and sixty pounds on bottom two cylinders all the plugs are good and bright, maybe possibly weak valve springs?? Also the cowling is pretty close to the rocker arms like maybe 3 or 4 m m or les from the rocker arms I'm thinking possibly enough to hit the rocker arms causing the push rods to come out in flight?? But that's not explaining the low RPM?? This engine used to have much more power than that and I don't know what has changed