Nissan NSF25A running at 2400 rpm @WOT

[CJovingo]

2 yrs ago we purchased a 2005 Nissan 25hp 4 stroke & to my ear sounded like RPMs were low @WOT. We have a 1989 Crest 28’ pontoon on lake with 25hp max limit. We are running a 9.9x9 prop that came on the Nissan when we bought it. Finally after 2 yrs, yesterday I installed a Altilaura tach & set it up. I found online that the Nissan NSF25A is 12 pole & set the tach accordingly I thought. Instructions weren’t very clear. There is a chart on the instructions for outboards that has poles & speed ratio. You press & hold button on backside of tach to enter setting mode on hour meter screen. Instructions then says to enter Value. I entered 12 (poles) but was I supposed to enter 6 (speed ratio) according to the chart? With value set at 12, tach shows motor idling at 600 RPM & 2400 at WOT. I thought RPMs were low but not that low. I figured I was going to get about 4500 RPM reading. Supposed to be 5000-6000 RPM @WOT. Going to try to go back to lake this week & reset tach value to the 6 (speed ratio) instead of 12 that I entered for poles. If that fixes my very low RPM reading I think it will read about 4800 RPM. If my tach reading is around 4800 after making changes to tach setting, is it worth changing prop? The prop chart for Tohatsu/Nissan only shows 1 other prop for heavy boat…10.2x8.3. From what I’ve read, decreasing pitch 1” increases RPM’s 100-150. I just don’t think .7” decrease is going to make that much of a difference. Especially if I need to go up 1000 RPM. Does diameter affect RPMs also, if I go from 9.9x9 to the 10.2x8.3? Is there any other adjustments that can be made to increase RPM besides prop swap? I’d like to get it in the mid-upper 5000 RPM. Any advice would be appreciated.

 

[CJovingo]

Here is screenshot of tach I bought

 

[pvanv]

No idea of speed ratio meaning.
avail props 8,9,10,11,12,13
Figure maybe 300 rpm per inch of pitch.
Diameter is insignificant.

 

[CJovingo]

Finally made it back to the lake yesterday & set the value on the tach to 6 (speed ratio). My idle is at 1000 rpm’s & 4600 rpm’s @wot. I ordered the only prop option available, the 10.2x8.3 to decrease my pitch. The .7” pitch decrease probably isn’t going to be worth the $170 spent.

 

[CJovingo]

I received my 10.2X8.3 prop 2 days ago & installed it today. Before swap with 9.9X9 prop I was at 4800rpm & 9mph (speed using gps app). With 10.2X8.3 prop I’m at 5200rpm & 11mph. 6 days ago I called marina where I purchased the used outboard before I got the new prop. He told me to call back after swap & he said he could send prop out to be custom pitched for like $120. Does this have possibility to damage the new prop? Should I have the prop repitched to get closer to 6000rpm? If .7” pitch decrease gave me 400rpm increase, would another 1.4“ decrease give me another 800 rpm? If I get it custom pitched, should I go with 1.4” decrease or should I go with like 1” to keep it just under 6000rpm? Thanks in advance for any advice.

 

[MattFL]

Talk to the shop that does the prop work, they will be able to give you better answers than you'll get here most likely. Make sure it's a shop that specializes in props and not just some guy.

 

[CJovingo]

Talk to the shop that does the prop work, they will be able to give you better answers than you'll get here most likely. Make sure it's a shop that specializes in props and not just some guy.

Thanks for the advice, I’m thinking about finding a shop on my own instead of going through my marina. Cut out the middle man.

 

[MattFL]

Thanks for the advice, I’m thinking about finding a shop on my own instead of going through my marina. Cut out the middle man.

Not a bad idea.

 

[CJovingo]

Not a bad idea.

Yesterday I called a boat repair place about 30 mins from me & they said there is one place in Ohio that does that work. Sante Marine Propeller in Cleveland Ohio/Lake Erie about 1hr 30mins from me. Gonna give them a call this morning when they open.

I checked out their website & they’ve been in business almost 75yrs. They repair most brand & styles up to 36”, so I think they know what they are doing. Some of services they offer,

• Skeg Repair
• Re-pitch Your Propeller
• Cavitation Plate Repair. Additional services include
• Custom Boat Shafting
• Shaft Straightening