25 Kohler with a lot of hours has lost a lot of power. I think the last time I changed the oil I used 10-40 vs. 10-30.............might have used straight 40w. I cannot come up with an explanation for the loss of power other than it might need a rebuild/repower. The mechanics that have looked at it can't either. I was wondering if the wrong oil could cause problems with the lifters which in turn would create a loss of power. Coils are fine.....compression is in limits, rpm's are at 3850, plugs are good. This has puzzled me and I don't think it's time to spend tha big dollars yet.......but I can't figure out why the sudden loss of power. I cut my yard yesterday with it and once it got hot it seemed to run somewhat better but still not 100% of what it could run. Can oil do this????