I need to know what the rpm is supposed to be wide open with this motor? Mine runs at 4750. The motor says 5250 max. Is this what it is supposed to run?
5250 would be your WOT (wide open throttle) rpm. If you're not reaching that, maybe a prop change is necessary. What kind of load are you carrying when you reach your top rpm? What kind of hull?
If you are happy with the performance 4750rpm is fine. The only thing you need to be conserned with is exceeding the max rpm for WOT. If you want to change your WOT rpm you could change the prop, reduce pitch, this would give you more pull out of the hole, increase acceleration, but at the cost of reducing top end speed.
Most boats you prop for that top rpm empty on a cool day and it goes fastest, and you never go over. If you want better holeshot(less pitch)for skiers maybe, or faster trolling(more) or whatever, then you can change it. Just do not go over that top rpm unless you are into performance racing mods and the like. More blades give better bite out of the hole and stabilize the boat some, but cost a little top speed.
Have a 97 120 hp. Specs say 5500 max rpm. Turning a 13 1/4 X 17 Merc Torq aluminum prop. Rpm max with it is 4800 and speed is about 35. Tried a 13 3/4 X 15 inch prop. Somewhat quicker on plane, rpm is about 5250 but speed dropped to 25. Very disapointing. Next try is going to be a SS prop. Was told to keep the same pitch and diameter prop as the 17 but w/ss the speed and Rpm would be greater. Will let you know when I test it.
