Prop / WOT question

[nodima]

I have a 25 HP 2 stroke on a 16.5 foot aluminum sea nymph. With just me in the boat I can get ~24.8 mph via my GPS, but the throttle is only at about the halfway mark. Further advancement of the throttle does not result in additional speed or a change in the motors pitch. The same thing happens with 4 people aboard, with a top speed dropping to ~21 or so.<br /><br />Does this indicate an issue with prop pitch? <br /><br />It does not have a tachometer, so I don’t know what my RPM’s are. I am planning to attach a “Tiny Tach” to the motor to give me a better understanding of it. Is this condition normal, or does it indicate something is amiss?<br /><br />Any thoughts?<br /><br />Thanks<br /><br />Nodima

 

[SCO]

Re: Prop / WOT question

If you can find the pitch from the prop and the gear ratio from the mfgr, then you can use a 10% prop efficiency loss and get an idea of the rpm your turning by using the exel spreadsheet... speed considering pitch rpm efficiency( use 10%) and gear ratio. If your in the max rpm range for your motor, probably ur getting full throttle, if below, then I'd suspect pitch too high or some other problem that robs power or a mechanical linkage setup problem w the throttle. <br /><br />First thing I would do though is take off the cover, find the throttle flapper on the carb, and see if it continues to open as you advance the throttle past the half way point.