About all you can do with that or any motor in a barrel is get it somewhere close. The procedure is simple. Start motor and run it at full throttle (if you can). Turn high speed needle to the right till it starts to lose power. Then turn it back to the left till it regains power.
As for the slow speed screw, just experiment with it for best idle. It screws in against a ramp, so good practice is to screw it in a bit with throttle open, then reduce throttle to see how it does. This is to avoid possible damage to the plastic ramp.
Final adjustment on a boat on the lake. Again, it is simple, not rocket science.
EDIT: I see you have a neutral-clutch model. Do not run fast throttle speeds in neutral. Must be in gear to prevent over-revving.
