# Engine will not rev above 2,100 RPM



## Ilenart (Jul 23, 2007)

Been having the above problem now for quite some time. Inititially thought it was the maximum RPM governor. However adjusted that today and still could not get the engine to rev higher than 2,100RPM when the engine is under load. 

Under no load the engine is happy to rev up to 3,500RPM where it hits the maximum RPM governor (which is actually just an adjustable bolt on the throttle). However as soon as the engine is in gear it will only go up to 2,100 RPM. You can advance the throttle further however it does not change anything.

I also do not think it is the wrong propeller as the previous owner measured the prop and took it to a specialist and the advice was that it was about the right size and pitch for the boat.

The engine is a 98HP Nissan SD33 diesel. Maximum RPM is 4,000RPM and maximum continuous RPM is 3,200. 

The engine should be easily able to get the boat up to hull speed (7.5kts) as the recommended engine for this boat is 50-80HP. At 2,100RPM the boat is doing 6 kts. I reakon if I can get the RPM up to 3,000RPM the boat should be pretty close to hull speed.

Anyone have any ideas why the engine will not rev above 2,100RPM?

Ilenart


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## SwanseaJack (Mar 11, 2008)

Not withstanding the measurements the previous owner made it really sounds like a wrongly pitched propeller. If that is the case you will be grossly overloading the engine so I would expect to see a lot of black smoke and it take a long time to rev up to the 2200. Are you seeing that?


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## Ilenart (Jul 23, 2007)

Nope, no black smoke and the motor revs straight up to 2,100RPM and then no higher.

Today we took the boat out and rev'd slowly up to 2,100. Then put the engine into neutral and the engine reved up to 3,500RPM no worries. Then put the engine back in gear and was back upto 2,100RPM within about 45 seconds. I played with the throttle a bit and it easily goes to 2,100 RPM but no higher.


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## svsirius (Jan 14, 2007)

If you are sure it's not the prop, then I would look at a fuel starvation issue. Change the fuel filters and maybe get the feed pump checked for flow volume. Odds are you are either putting too much load on the engine [prop] or not getting enough fuel to it to allow full throttle.


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## chucklesR (Sep 17, 2007)

If no load RPM is 3500 and loaded maxs RPM at 2100 it's the prop.

The ONLY difference is the load on the engine, ergo the cause is the load on the engine. Life really is that simple.

OTOH, if max rated RPM is 4000 you should be able to hit 4000 with no load. That means that fuel starvation or air starvation might also be issues. My bet is the PO upsized the engine without consideration for the supply side. Of course he might also have put a monster alternator on it which is overloading the engine but you haven't mentioned one.

Nothing in the world of sailing gets you in more trouble that believing the previous owner without question (e.g. "the rigging is fine, don't worry about the rust marks" is right up there with "I measured the prop and it's correct")


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## JohnRPollard (Mar 26, 2007)

Ilenart said:


> I also do not think it is the wrong propeller as the previous owner measured the prop and took it to a specialist and the advice was that it was about the right size and pitch for the boat...Ilenart


Get a second opinion from a new expert. Clearly the P.O. was having a problem if he sought advice -- unfortunately is sounds like that advice was perhaps less than scientific. Prop pitch is almost a black art, and opinions vary. My guess is that the prop is over-pitched.

For your consultation, have the prop size and pitch in hand, as well as other important specs (engine hp, red line, displacement, etc). Also, sometimes props lose or gain pitch from the original spec and need to be re-tuned, so the specs may no longer be accurate.


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## mallo (Mar 21, 2007)

I don’t know if this will help but I have fitted several Max Prop propellers (and are very satisfied with them including several customers), when they came down from the manufacturers they had a setting that they should be set for that vessel/engine and I have normally set them up at that, however most of them we have had to re-set them slightly one way or another.
In one instance we pitched the prop more and the boat gained about a knot extra speed, but the engine revs were down from 3400 flat out to 2800, the friend was very happy as he could now keep up with us!!, but the engineer who looked after the boat said it was overloaded, however its run like that for over 10 years without any problems.
On our boat, which is a similar size, engine is a ford 90bhp and we only get 2000 rpm at best however it’s a much lower revving engine (max cont revs 2500) and at 2000 rpm we are getting 8.5 Knots.
When we first fitted the prop, on the settings from the manufacture we were getting 2300 rpm but only 7.5 Knots, we pitched the prop a degree more and gained the extra speed and less revs, we hardly ever run the engine over 1800 rpm and for more fuel economy (while the price is high) we have been running it 1500 rpm giving the said 7.5 Knots.
It sounds like an incorrect prop size, what it the ratio of the gearbox and what size prop do you have?
Also could it be a problem in the gearbox and as suggested by others a fuel starvation? How clean is the bottom/prop? I knew someone who had a shortage of power under load and go the fuel pump re-calibrated and all of a sudden regained the lost revs (I think it was about 5-600) it could be this that causing your problem.
Go to the boat manufacturers and see what prop should be on this set-up, or a well established prop manufacture should be able to give you a guide.
I hope this helps, sorry to go on a bit.
Please let us know how you get on
Best wishes
Michael


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## jrd22 (Nov 14, 2000)

You said the governed (max) rpm is supposed to be 4000, but you are only getting 3500, I think that is part of your problem. I'm no expert on this engine but I really doubt that the governor is an adjustable stop screw. The governor should be an internal mechanism in the fuel injection pump. I would get the manual or consult a dealer for the engine, but I don't think you are getting full throttle/HP. You should be able to get 4000 no load. By restricting the throttle with that stop screw I think you are limiting the inj. pump from delivering enough fuel.

John


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## Valiente (Jun 16, 2006)

You'll need to approach this step-by-step. It sounds like the prop to me, but it could be "all of the above" creating what looks to be a single-point problem, if you see what I mean.

Large alternators overtensioned and foul bottoms could easily steal a few hundred RPM. What is your RPM at idle, by the way?


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## negrini (Apr 2, 2008)

Being really simple, are you sure your throttle cables are running freely and well adjusted to WOT ? Then, check your prop system with a trusted mechanic. Then, check engine compression.


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## Brucerobs (Mar 12, 2007)

*Fouled prop/shaft*

While this might sound overly simplistic, I had similar symptoms last year and found my prop and shaft to be fouled with barnacles, even with very regular use. I couldnt get the RPMs up. At least worth a check if its been a while since youve seen it.


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## Ilenart (Jul 23, 2007)

Thanks for all the replies.



> If you are sure it's not the prop, then I would look at a fuel starvation issue. Change the fuel filters and maybe get the feed pump checked for flow volume. Odds are you are either putting too much load on the engine [prop] or not getting enough fuel to it to allow full throttle.


Svsirius, I checked the fuel filters about a monh a go and they were clean. I have two fuel filters and today I tried turning them both on and it made no difference. So unless the fuel is being restricted somewhere besides the fuel filters this is not the problem. Also I would of thought with fuel starvation the engine would start missing or run uneven. This does not happen; the engine just runs up to 2,100 RPM and then no higher.



> OTOH, if max rated RPM is 4000 you should be able to hit 4000 with no load.


chucklesR the engine is reving to 3,500RPM with no load and then is hitting the mechanical adjustable stop screw. If I adjust this out I am fairly sure the engine will rev higher with no load.



> I knew someone who had a shortage of power under load and go the fuel pump re-calibrated and all of a sudden regained the lost revs (I think it was about 5-600) it could be this that causing your problem.


Mallo, this could very well be the problem.



> You said the governed (max) rpm is supposed to be 4000, but you are only getting 3500, I think that is part of your problem. I'm no expert on this engine but I really doubt that the governor is an adjustable stop screw. The governor should be an internal mechanism in the fuel injection pump. I would get the manual or consult a dealer for the engine, but I don't think you are getting full throttle/HP. You should be able to get 4000 no load. By restricting the throttle with that stop screw I think you are limiting the inj. pump from delivering enough fuel.


JRD22, it was my mechanic who spotted that the max RPM governor was a simple adjustable stop screw. Like you I was looking for something more complicated (the engine manual specifies three different way depending on the fuel pump used) and my mechanic looked at it and said "nah this is it". Note that the engine is almost 30 years old. Last week with my mechanic we adjusted the stop screw and that increased the no load max revs from 2,500 to 3,500. I'll try adjusting it again, however my guess is this is not the problem.



> You'll need to approach this step-by-step. It sounds like the prop to me, but it could be "all of the above" creating what looks to be a single-point problem, if you see what I mean.
> 
> Large alternators overtensioned and foul bottoms could easily steal a few hundred RPM. What is your RPM at idle, by the way?


Valiente, the bottom is a bit fouled, however this has been a problem / issue with the boat for the last 3 plus years. Even when the bottom is freshly painted this has still been an issue. Still I need to go for a swim so I'll add this to the list of things to try.

There is a number of alternators / pumps running off the engine. However the engine is really oversized for the boat (the recommendation for this boat is 50-80HP and this engine is 98HP). So I don't think this is the problem.



> Being really simple, are you sure your throttle cables are running freely and well adjusted to WOT ? Then, check your prop system with a trusted mechanic. Then, check engine compression.


Negrini, cable adjustment is fine. Today my wife was throttling while I was looking at the engine and it was all running fine. Ill add checking engine compression to the list.

For everyone who suggested rechecking the prop specifications; yep that's what I have been thinking as well. The previous owner may of got it wrong so it's worth rechecking. This was the first thing my mechanic suggested to check as well.

Thanks for all the suggestions. I'll keep this thread up to date with how the investigations are going. My mechanic is really busy at the moment so its probably going to take a couple of weeks before we can try out some of the ideas.

Ilenart


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## timebandit (Sep 18, 2002)

I have to agree with these people.

The stop screw you talk about is like putting a board under your gas pedal for gas millage and then expecting your car to pull a trailer up a hill at full speed. If you don't open the throttle all the way you will not make the power you need!!

I would try taking the boat out and then put in gear and adjusting the stop under load untill the desired rpm is reached. After that , try placing it in neutral and slowly rev to see where it stops. It's free and you get to go out sailing.

If the motor still does not come up to speed under load then look elsewhere.

Rick

Quote:

OTOH, if max rated RPM is 4000 you should be able to hit 4000 with no load. 
chucklesR the engine is reving to 3,500RPM with no load and then is hitting the mechanical adjustable stop screw. If I adjust this out I am fairly sure the engine will rev higher with no load.

Quote:

I knew someone who had a shortage of power under load and go the fuel pump re-calibrated and all of a sudden regained the lost revs (I think it was about 5-600) it could be this that causing your problem. 
Mallo, this could very well be the problem.

Quote:

You said the governed (max) rpm is supposed to be 4000, but you are only getting 3500, I think that is part of your problem. I'm no expert on this engine but I really doubt that the governor is an adjustable stop screw. The governor should be an internal mechanism in the fuel injection pump. I would get the manual or consult a dealer for the engine, but I don't think you are getting full throttle/HP. You should be able to get 4000 no load. By restricting the throttle with that stop screw I think you are limiting the inj. pump from delivering enough fuel. 
JRD22, it was my mechanic who spotted that the max RPM governor was a simple adjustable stop screw. Like you I was looking for something more complicated (the engine manual specifies three different way depending on the fuel pump used) and my mechanic looked at it and said "nah this is it". Note that the engine is almost 30 years old. Last week with my mechanic we adjusted the stop screw and that increased the no load max revs from 2,500 to 3,500. I'll try adjusting it again, however my guess is this is not the problem.


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## jrd22 (Nov 14, 2000)

The reason why I question whether you are getting full throttle is that you said that there is no black smoke and you didn't mention the engine getting hot while at full throttle (2100rpm) and below hull speed. If your inj. pump was delivering enough fuel for full power and you were only getting a little over 50% of total rpm's there should be a lot of smoke and heat. What you are descibing is exactly how an engine that is not getting full throttle acts, it will go quickly to 2100, no smoke, no heat, no sign that the engine is working hard at all. That's why I don't see how it could be an overpitched prop or foul bottom, etc. There are adjustable stops on engines for generators, so you can fine tune the rpm for voltage, but I still don't think that is the governor for your engine, unless I am misunderstanding your description. Just getting 3500 or 4000 rpm under no load does not mean that you are getting full throttle under a load. If it were me, I would back that stop off all the way and try motoring and see if it increases rpm and speed, just don't exceed 4000 rpms.
By the way, none of my mechanics at work has ever heard of a diesel with an adjustable stop screw as a governor.

Good luck, John


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## KeelHaulin (Mar 7, 2006)

I have a similar feeling as JRD22; a throttle stop is not a "governor". A governor is a device that maintains constant RPM regardless of load. So in an example of say a tractor; if you run the engine up to 2000 and then engage the drive the engine should maintain it's RPM regardless of the fact that you put the load on it. The governor will automatically increase the fuel flow to compensate. That can't be accomplished with a stop screw; it's an internal flow control on the fuel injector. I'm not sure how you adjust that; or if you can adjust it.

I would go back to looking for a fuel flow restriction or a problem with your driveline. If your tank has an internal screen at the fuel intake the screen might be clogged with growth (a common problem with diesel tanks). That would prevent max flow even if your filters are clean. You could have a bad bearing in your transmission, a bad cutless bearing, or a grossly mis-aligned engine; any of these could cause engine overloading.


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## SwanseaJack (Mar 11, 2008)

Ummmm, thinking here.... Its not just that the rev counter is reading low when in gear because of something going on in the wiring loom is it? I have seen something like this once when an oil pressure sender wire was mixed up with the rev counter. Is the engine actually running slow?


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## cardiacpaul (Jun 20, 2006)

you are over pitched or sized on the prop. 
older diesels would belch black smoke if overloaded mainly because they uesd rack rail injectors fed by a strictly mechanical pump. 

Newer (late 90's & newer) don't because of the governor and rpm senders are limiting "pollution" of unburned diesel. 

take an inch off the pitch and an inch off the diameter, and you'll see big changes.


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## recycle (May 6, 2008)

Could be a clog in the exhaust and water mixing elbow.


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## Ilenart (Jul 23, 2007)

jrd22 said:


> The reason why I question whether you are getting full throttle is that you said that there is no black smoke and you didn't mention the engine getting hot while at full throttle (2100rpm) and below hull speed. If your inj. pump was delivering enough fuel for full power and you were only getting a little over 50% of total rpm's there should be a lot of smoke and heat. What you are descibing is exactly how an engine that is not getting full throttle acts, it will go quickly to 2100, no smoke, no heat, no sign that the engine is working hard at all. That's why I don't see how it could be an overpitched prop or foul bottom, etc. There are adjustable stops on engines for generators, so you can fine tune the rpm for voltage, but I still don't think that is the governor for your engine, unless I am misunderstanding your description. Just getting 3500 or 4000 rpm under no load does not mean that you are getting full throttle under a load. If it were me, I would back that stop off all the way and try motoring and see if it increases rpm and speed, just don't exceed 4000 rpms.
> By the way, none of my mechanics at work has ever heard of a diesel with an adjustable stop screw as a governor.
> 
> Good luck, John


John, my guess is that you are on the right track RE: the engine is not getting sufficient fuel to rev above 2,100 RPM. The engine does not appear to be laboring or overheating, which is why I'm thinking the prop is not the problem. Will talk to the mechanic and get his opinion, but I will be looking at the fuel injection pump first. If that's not the problem will start checking out prop pitch, compression, etc.

Ilenart


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## Ilenart (Jul 23, 2007)

SwanseaJack said:


> Ummmm, thinking here.... Its not just that the rev counter is reading low when in gear because of something going on in the wiring loom is it? I have seen something like this once when an oil pressure sender wire was mixed up with the rev counter. Is the engine actually running slow?


When the engine is idling its reading around 600-700 RPM, which is the correct idling speed. Also if the engine was actually reving faster we should be getting closer to hull speed of 7.5 knots, rather than the six knots.


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## Idiens (Jan 9, 2007)

If the gearbox were having a lubrication problem, it could also load the engine when in gear....

Also, what type of stuffing box do you have? Overtight?


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## timebandit (Sep 18, 2002)

What happend to the boat between these two posts??



Ilenart said:


> Been having the above problem now for quite some time. Inititially thought it was the maximum RPM governor. However adjusted that today and still could not get the engine to rev higher than 2,100RPM when the engine is under load.
> 
> Under no load the engine is happy to rev up to 3,500RPM where it hits the maximum RPM governor (which is actually just an adjustable bolt on the throttle). However as soon as the engine is in gear it will only go up to 2,100 RPM. You can advance the throttle further however it does not change anything.
> 
> ...




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04-27-2008 - [add post to favorites] 
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Boasun









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*Sea Suctions or Keel Coolers*



Here in the southland of the USA practically every comerical vessel uses keel coolers. Two advantages for them are you are not sucking in sediment & other scud, and you don't have sea strainers to clean all the time. You have a hump on your hull that may be slowing you down about a quarter knot more or less. One boat I saw, was using about two feet of copper tubing, sticking out along the hull in a hair pin shape, for its generator's cooling coil. There are comerically made hull coolers that come in all shapes and sizes.​
With Sea Suction, you may have a sea chest where the main, generator and fire/wash down system draws its water. Hopefully you have heat exchangers and are not sending raw water through your engines. But you still have to have sea strainers and those heat exchangers have to be cleaned every now and then. But you don't have a hump on the bottom of your hull adding to the hull friction of passing throught the sea. Also with sea suction you may have that sea chest or a separate hole through the hull for each piece of machinery that needs cooling...​
Most sail boats have sea suction... But what would you prefer?

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04-28-2008 - [add post to favorites] 
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Ilenart









Roberts Classic 45
​Join Date: Jul 2007

Location: West Australia

Posts: 111

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​
My yacht has keel coolers installed, approx 1 inch diameter pipes in a set of three. Works fine, the setup is 29 years old and still working no problems. My mechanic said he sees a lot of keel coolers on fishing boats.

Note that I still have a raw water inlet that cools the gearbox and then is injected in the exhaust manifold. The manifold had to be replaced a couple of years ago, however I would'nt expect much more than 5-10 years given the combination of hot gases and seawater. This also supplies water for the washdown, generator and sink.​
Disadvantages are more maintenance with scraping / sanding down the pipes, priming and painting. Can be difficult reaching the top of the pipes and I guess they will eventually wear out and need replacing. Never thought about the drag from the pipes, however my boat has a sail area of 1,011sq ft (SA/disp of 17.2) and a 98HP diesel so reaching hull speed has never been an issue / concern. Also compared to the drag from my keel it is probably pretty minor​
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## Ilenart (Jul 23, 2007)

Timebandit, you have a good eye for detail!

Only recently realised that hull speed on my boat was 7.5 knots. Previously thought that 6 knots was around hull speed. 

On some other post there was discussion on how you should periodically rev your engine to full power as running on half speed all the time is not good for a diesel engine. I then worked out that my engine is only running at 50% maximum revs all the time, which got me thinking about hull speed, etc.

Ah well sprung


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## Idiens (Jan 9, 2007)

Ilenart - are you measuring your hull speed with a log or with GPS?


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## Ilenart (Jul 23, 2007)

> If the gearbox were having a lubrication problem, it could also load the engine when in gear....
> 
> Also, what type of stuffing box do you have? Overtight?


Idiens, prop shaft and seal was replaced about three years ago. When the boat was last hauled about six months ago the prop freely spun by hand. Therefore I don't think this is the problem.



> Idiens Ilenart - are you measuring your hull speed with a log or with GPS?


Speed is measured by GPS, which I am fairly sure is accurate.


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## groundhog (Jun 27, 2006)

Sorry in advance if this is already covered... I'm not going to read all of the posts here...

...but, make sure you are not over-propped, or barnacles on prop.


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## tdw (Oct 2, 2006)

Ilenart,
I know I'm repeating what others have already told you but the new thing had the same problem after she was re-engined and it was the propellor.
cheers


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## Lullaby (Dec 27, 2020)

Can anyone


Ilenart said:


> Been having the above problem now for quite some time. Inititially thought it was the maximum RPM governor. However adjusted that today and still could not get the engine to rev higher than 2,100RPM when the engine is under load.
> 
> Under no load the engine is happy to rev up to 3,500RPM where it hits the maximum RPM governor (which is actually just an adjustable bolt on the throttle). However as soon as the engine is in gear it will only go up to 2,100 RPM. You can advance the throttle further however it does not change anything.
> 
> ...


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## Lullaby (Dec 27, 2020)

was there an outcome here? I have the same issue, same engine, done the same checks. Thanks


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## MarkofSeaLife (Nov 7, 2010)

Lullaby said:


> was there an outcome here? I have the same issue, same engine, done the same checks. Thanks


Ummmmm the thread was from 2008.

Everyone officially died years ago.

Start a new thread with your own exact problem 

Mark


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