02 225 ox66, can't reach full rpm's

[Moose]

Im running with a 17 pitch merc prop 3 blade. I've already replaced the oxygen sensor, fuel filter, and water separator. I just started running ring free and sprayed power tune into the carbs yesterday to free up some carbon build up. I'm only able to reach 4800 rpms. It seems like she moving at the right speed for the rpms she's pushing. I'm sort of new to working on motors so I don't know all the parts or names so try to bear with me. Any information would be greatly appreciated.