Recently purchased an oversized Johnson 120 that was supposed to have been rebuilt 4 years ago, VRO removed. Mounted on a 17' bow rider.
First thing replaced complete impeller housing and hoses. Compression is not within the 10-15% range. Marine Mechanic reading was 121 on both left side and 139 on both right side yet motor still runs very well. Would carb cleaning help out at all?
What would it typically take to correct this? New ring kit? What risk am I taking by running it this summer as is?
Side story: Lost stainless prop on test run (MAX 40 MPH) before I was able to take an RPM reading. Replaced with Aluminum prop with same 23 pitch but now I'm at (MAX 34 MPH) at 4,500 RPM. Considering a replacement to 21 pitch as it is much slow to come off plane now. Not sure of the standard RPM range for this engine...5,500 ?
Am I correct in assuming that I should be able to attiain 50 + MPH with this engine if compression and propulsion were corrected?