Buy your plugs at the local auto parts store, like AutoZone, NAPA or Advance Auto. Usually MUCH cheaper than buying from a marina or somewhere online.
I have no idea of the gearcase ratio of that motor, or the weight and water resistance of your boat. You have to start with what you have.
What pitch do you have now, and how does it perform? What is your RPM at top speed?
Take it for a run. With the trim a little on the down side, slowly start trimming the engine up, bit by bit. Your speed should increase each time, until either the bow starts bouncing or the prop starts ventilating (sucking air) Trim it back down just enough to stop and record your speed and RPM.
THAT number will be your WOT (Wide Open Trim) speed as your boat is currently rigged.
Once you know that, IF you are not happy with the performance, post those numbers and others can help you see if a different prop will help.
FOR WHAT IT"S WORTH, sometimes people follow the above directions, and their boat goes faster than it ever has, and they realize that they had just never figured out the best trim angle before.
I hope it works out.
