You can advance the throttle in neutral by depressing the center pivot point cover on the throttle lever. Push in on that cover and you will feel a button being depressed. That button disengages the gear shift cable and allows you to advance just the throttle cable as much as you want. Try doing the test again with the motor warmed up, the plugs removed, and the throttle plates wide open. You should see 115-125 psi in each cylinder.
Mike ....... Miami, FL