96 GTX compression test results advice needed

[artr]

I just ran a compression test before winterizing my ski. I pulled both plugs out, put the wires on the grounding posts, had the throttle fully depressed while cranking. I got 155psi on the MAG cylinder and 107psi on the PTO. The ski ran fine all summer, just a little hard starting in the water (usually the 2nd try unless warm, then would start right up). I had measured about 145 last year on both cylinders but did not hold the throttle open. The thing that I need advice on is the the engine cranked smoothly when measuring the MAG side, but chugged (was shaking more and sounded funny) when measuring the PTO. Engine cranked smooth with plugs out and nothing blocking cylinder holes. Put the plugs back in and it fired right up at the touch of the start button. Is there something else at play here or is that the type of behavior you get when one cylinder starts to fail? What else should be looked at or tried? Thanks.

 

[artr]

Sorry, my mistake. I am using an older compression tester that has a rubber tip that must be held and pushed into the plug hole. When I tried it later today, I pushed a lot harder and read 150psi on both cylinders. The tester must have been getting pushed out of the plug hole and the roughness and sound was the compression partially escaping while cranking.