pontoon 7m with honda bf90

by tywiesz
(gold coast, australia)

Hi, situation is; bought a boat with 3200rpm at WOT. Idle 450 so thought must be the gauge, replaced it and now idle 1200 rpm and at WOT 4800 rpm.s Is this boat over propped? coz it does not go to at least 5600 rpm's? Or as it is a new boat to me (boat 10y old maybe less, previous owner not available to ask questions) how do I know if the engine actually can still provide/go 6000 rpm's? so, is it over prop or engine? Maybe both, I thought to this:

go full throttle and start trimming up a bit by bit till I see something,

so while trimming the outboard up my rpm's were increasing and increasing till total cavitation and big lose of a speed at 5600 rpm's. Is this the max what the motor can do? if this is 400 rpms short of 6000 rpms than that would have been 4800 +400= 5200 at WOT for current condition, is this still over prop?

What do you guys think? I noticed the prop got "lips" dunno how to call it, the prop blades outer ages a bit profiled to combat this boat easy cavitation. Should I un-profile the edges back to normal, than I would lose the water grip and maybe cavitate at 3000. There is hydrofoil plate installed to help the cavitation already. Grrrr, that is what happens with used boats, full of problems and mysteries, isn't? cheers. T