RPMs not reaching cruising speed

Scott T

New Member
Feb 22, 2018
3
Boat Info
2006 Sundancer 260
Engines
Mercruiser
Anyone have advice ort point me in the right direction.
Upon starting out I throttle up slowly ( as well as trim the boat out ) but she will not get over 3200 RPMs, even at full throttle. Oil and fluid levels look good.
Sundancer 260 heavy boat for the single engine but has happened several times
Have had her cruising at 3800 - 3900 RPMs @ 25kts or so
Thanks

Scott
 
Not sure where you boat, but when is the last time the bottom was cleaned? Makes a bigger difference than you'd think if it's full of growth. If that isn't the issue then I would be on to diagnosing why you are down on power, tune up, bad fuel, smartcraft, etc.
 
Boat in Atlanta and is in a wet slip with some growth on it no doubt ... Will inquire about a tune up
but not sure what you refer to "smartcraft?"
Thank You for replying !
 
Do not underestimate how much growth on the bottom and drive will slow the boat down. Get the boat hauled, pressure washed and put back in and run it. Until that is done you will be guessing.
 
Also, check that you don't have any hose leaks down below.
On the way back from Provincetown, she blew a hole in the raw water hose. For whatever reason, no alarms went off. However, the system recognized the loss of pressure and put itself in to 'limp mode' I forget exactly the rpms I was limited to. I replaced the fuel filter, and was pretty dumbfounded until I noticed water in the engine compartment that is never there. We had to fix the hose MacGyver style to get home, as the part wasn't available for days.
This was on my 2006 260.
And yeah, with people, and snotty conditions, she can take a while to plane out with the 350 mag anyway.
That boat would be sick with a 496
Good luck!
 
If you verify that the bottom condition is not the problem...

You should be getting into the high-4,000 RPM range easily and 40+ MPH. Before you change any components (although checking plug condition is easy and free), check fuel pressure while running.
 
Thanks Nick, doesn't appear to be any leaks .... when I get her out of the slip and get it out in the lake she will not get over 3200 RPMs ..... and will never beep at me indicating an "engine overspeed" issue ...... When tied up at the slip and in Neutral, I can rev it up to 3500 and starts beeping and indicating an engine overspeed ..... I am set to have her lifted and power washed soon to eliminate that possibility, not mention, she needs it after sitting for a couple months
 
Engine overspeed at 3500rpm? Doesn't sound normal.
 
Engine overspeed at 3500rpm? Doesn't sound normal.

It's because the computer knows the engine is in neutral and doesn't like the combination of neutral and higher revs.
 
Nobody likes a dirty bottom:)
That could be it.
Mine would also beep when revving in N too.
Good luck!
 
Clean Bottom, plugs check out good, consider dirty fuel injectors. Removed and had mine professionally cleaned - 496 mag X2, RPMs from 3200-3300 to 4250. Of the 8 injectors on each motor - 10 were better than 50% blocked, with 3 only allowing 20% through. Major difference in power, planing time and top end. Before cleaning speed at WOT 33 mph, would get to about 3/4 throttle and still have some left, between 3/4 throttle and WOT there would be no increase in rpms. After cleaning speed at WOT - 44 mph with a light load.
 
@Scott T , I realize this is an old post but I’m having the same issue and was wondering what was causing your RPM problem?

matt
 
@Scott T , I realize this is an old post but I’m having the same issue and was wondering what was causing your RPM problem?

matt
There are multiple reasons for your issue. Meaning, IF we hear back from Scott with a resolution there's no more of a chance that it is YOUR issue than something else. Take a look through the thread - there's a number of things noted to get you started.
 
Last edited:
Thanks for your reply as I had read through the threads.

turned out my father in law added to much oil during an oil change

I sucked out 2 quarts and power and R’s returned back to 4K easily

now onto the tune up as I believe the 05’ 260 Sundancer should be turning 4500 to 5 R’s in calm water
 
when was the last time your props were tuned? that makes a massive difference, also like stated above there could be issues with fuel delivery check fuel pressure on the rail.
 

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