Low RPM under load at full throttle

[patrscoe]

I pulled the exhaust elbow and it looked clear. The overall elbow and hoses look to be less than 10 yrs old or newer.
I retested the RPM in idle and I was able to reach 3100 rpm.

I spoke to the Yard Master and reviewed where I am with the problem. and although it is not preventing me from sailing this season, I would like to resolve by the end of this year. His opinion is that injectors and injector pumps are not the cause of the issue. I would see hard starting and more loss of power, not just reaching top RPMs. But said it is worth removing the injectors and injector pump, send them out to be cleaned and adjusted, and it will improve your engine's performance, as they are probably in need of this.
Since the exhaust elbow was cleaned, which he was doubtful as he would be surprise if I would have reached 3100 RPM in idle.
He is leaning towards my new prop and although I don't have black smoke, it is common to be a degree or two off, and sometimes a new prop may not be at the correct pitch.
So instead of repitching my new prop and guessing, I am going to do a short haul next week, remove the new prop and put on my old fixed 2 blade prop and have them clean the bottom, and start over - if this works, then it was my new prop.

 

[Loren Beach]

So instead of repitching my new prop and guessing, I am going to do a short haul next week, remove the new prop and put on my old fixed 2 blade prop and have them clean the bottom, and start over - if this works, then it was my new prop.

The better boat years have a ship wright named "Occam".....

 

[Christian Williams]

I had my injectors serviced. Report here.

 

[Pete the Cat]

I pulled the exhaust elbow and it looked clear. The overall elbow and hoses look to be less than 10 yrs old or newer.
I retested the RPM in idle and I was able to reach 3100 rpm.

I spoke to the Yard Master and reviewed where I am with the problem. and although it is not preventing me from sailing this season, I would like to resolve by the end of this year. His opinion is that injectors and injector pumps are not the cause of the issue. I would see hard starting and more loss of power, not just reaching top RPMs. But said it is worth removing the injectors and injector pump, send them out to be cleaned and adjusted, and it will improve your engine's performance, as they are probably in need of this.
Since the exhaust elbow was cleaned, which he was doubtful as he would be surprise if I would have reached 3100 RPM in idle.
He is leaning towards my new prop and although I don't have black smoke, it is common to be a degree or two off, and sometimes a new prop may not be at the correct pitch.
So instead of repitching my new prop and guessing, I am going to do a short haul next week, remove the new prop and put on my old fixed 2 blade prop and have them clean the bottom, and start over - if this works, then it was my new prop.

I agree with your yardmaster. Doing what you are doing is cheaper than servicing the injector pump or injectors and--if the problem started with the new prop and you can get full RPM in neutral I doubt it is the problem. I would just say that new props are often pitched incorrectly. This is one of those science/art things that are rapidly going away. While you have the boat out of the water: check to make sure that you have a couple inch gap between the prop tips and the hull: it is possible to have wild cavitation if there is not enough clearance that will inhibit speed and RPMs. You generally want to swing the biggest prop you can with a decent gap and adjust the pitch to allow your engine to make max rpm at max hull speed in flat water.

 

[Pete the Cat]

I had my injectors serviced. Report here.

Well that is interesting. You indicate that the injectors were giving a proper pattern (I am always a bit skeptical of what they mean when that is observed--mostly that it aerosolizes and no drips I suppose) and I assume there were no drips from any of them[--which is a sure sign of a problem. I have never understood exactly what is done to injectors to "clean and overhaul" them--but, like injector pumps, we shade tree mechanics should stay away from taking them apart. I do not have extensive experience, but I am thinking that you might have unintentionally done something else that made the difference in starting and fuel consumption in just taking things apart. I recently "fixed" a balky starting 25XP into a split second start up with 10 second glow by simply cleaning the grounding lug on the engine--which looked fine from the outside, but was just a tad corroded when removed. Undoubtedly, the problem was simply the ground for the glow circuit was just a tiny bit inconsistent. In my cruising years, I seemed to have a quite a few "fixes" I supposedly effected for folks where I was not exactly sure what I had done to correct the problem, but there was little doubt that things had improved. I accepted the thanks, but wondered occasionally about what might have been the real problem. I was never lost for a theory however.. FWIW.

 

[Loren Beach]

Regarding the injectors, it's my understanding that when tested they look for a even spray pattern, as opposed to too much diesel hitting one side and trying to get past the rings.
I had this done (and new tips were not very expensive) on our previous diesel at about 1000 hours.
Actually the biggest single bit of preventative maintenance I ever did on that engine was to have the starter rebuilt --- suddenly it turned over a LOT faster!

 

[Christian Williams]

Me too on the starter.

I have to admit that few people who service injectors do not report a big improvement. And when I wash my car it goes faster.

In my case it was deciding to hold down the starter button longer, thereby helping the diesel to get going, than anything else I tried. Andit actually solved all my slow-start issues. But I think I should keep this quiet, as a bit embarrassing....

 

[patrscoe]

If it costs $50 to have them rebuild, would it make sense to purchase new Kubato injectors, which costs $80?
I saw a thread on Sailnet that someone purchased Kubato injectors as a replacement and I reached out to him, which he gave me the new part number. Appears that they worked well.
Sounds like a winter project.

I have not thought about the possiblity that the prop tips are too close to the hull. That also makes sense. I will look at that too.
Some research, apparently you need a minimum of 15% the diameter of the prop, 20% recommended. So I should be looking at a min of 2 1/4" to 3" clearance.


One benefit of seeking a solution to a engine problem, you end up doing a lot of maintenance and replacements. I was looking at my engine the other day and thinking it looks better than when I purchased it. Just need to get to a resolution to the problem.

 

[Pete the Cat]

If it costs $50 to have them rebuild, would it make sense to purchase new Kubato injectors, which costs $80?
I saw a thread on Sailnet that someone purchased Kubato injectors as a replacement and I reached out to him, which he gave me the new part number. Appears that they worked well.
Sounds like a winter project.

I have not thought about the possiblity that the prop tips are too close to the hull. That also makes sense. I will look at that too.
Some research, apparently you need a minimum of 15% the diameter of the prop, 20% recommended. So I should be looking at a min of 2 1/4" to 3" clearance.


One benefit of seeking a solution to a engine problem, you end up doing a lot of maintenance and replacements. I was looking at my engine the other day and thinking it looks better than when I purchased it. Just need to get to a resolution to the problem.

Yes, your calculations are correct for gap between the hull and the tips--you can push it a bit--the downward angle will help reduce cavitation. My Tartan is OK with about a 10% gap but a downward angle. You do want to swing the biggest diameter prop you can fit there--but with the proper pitch. I think you are likely going to find the problem in the pitch, but I will be interested in what you find out. I am not experienced enough to render an opinion on the injector issue--new or rebuilt. I agree with Christian that in the folks who have replaced injectors, they have not generally found a lot of improvement--they seem most likely to fail catastrophically from what my old grizzled mechanic friends have said--and I only had one fail because I dropped it on a cement floor--never had a failure in service or found it as the fault of engine not running properly. In my cruising years, I carried a spare, but never needed it. It is a little difficult for the amateur to see the spray pattern because your really should not bend the fuel line to the injectors--it is a very precisely measured (diameter and length), but yes they are looking for a nice oval shape to the spray and no drips. Racor filters really keep injector problems to a minimum. And the low sulfur diesel fuel is much cleaner than the stuff we used a decade or two ago.
I am a proponent of doing your own work on your engine as you have done. Diesels are remarkably simple machines and being familiar with them, particularly if you are going cruising, seems like important preparation.

 

[Kenneth K]

I have not thought about the possiblity that the prop tips are too close to the hull. That also makes sense. I will look at that too.
Some research, apparently you need a minimum of 15% the diameter of the prop, 20% recommended. So I should be looking at a min of 2 1/4" to 3" clearance.

I wrestled with the prop tip clearance issue when I shortened my prop shaft 2 years ago. I remember those ballpark 15-20% numbers you quoted.

Initially, my prop extended over 4" past the end of the cutlass bearing (one shaft diameter, or 1" extension is the general rule of thumb here). I reduced the extension down to about 1.5" but didn't want to risk going further. With the shaft shortened, there is little more than an inch clearance between hull and the prop tips now. Two years later, I've noticed no vibration, noises, prop wear, or wearing away of paint/fiberglass on the hull above the prop. I read that all of those can be signs of cavitation from too little prop clearance. I definitely did not notice a reduction in engine RPMs after shortening the shaft.

My guess is prop tip clearance is not related to your problem.

Old.

New.

 

[patrscoe]

Thanks for all the replies and input. I know this thread is going on longer than it should but it has been helpful to bounce troubleshooting concepts off of everyone and I really appreciate it.

I created a list of what has been done and what possibly could be researched.
Fuel Delivery System:
Completed Tasks
- All fuel hoses have been replaced and associated clamps and fittings from the fuel tank to the injector pump. System seems tight.
- Bleed valve was removed, cleaned and reinstalled with the knob tight to the nut.
- Replaced the old Racor fuel filter assembly with a 500 series. (note: one of the extremely difficult process of finding a air leak last year was in my older Racor alum bracket. When I removed it completely, I saw a hairline crack on the backside).
- Removed, cleaned and replace the screen in the round Gold fuel lift pump.
- Removed all fuel, whip tank bottom clean and added fresh fuel for spring
- All new fuel filters
Not done
- Replaced fuel lift pump? seemed okay and provides pressure. Engine does not start hard.
- Service fuel injector pump and injectors? I was going to wait until the winter, while the sailboat is on the hard
- I have nothing else on the fuel side

Propeller and Etc...
- New cutless bearing and stuffing box (repacking) was replaced 3 yrs ago and appears to be in good condition
- New prop was installed during the winter; the prop is a 2 blade 15x10 FOF and my previous prop was the standard 2 blade fix 15x11.
- 1" pitch equals +/-200 rpm, and having a max RPM of 2000 to 2100 with a clean bottom and prop, that does not sound like that is the issue. The prop pitch would have been 3" to 4" off. Also it has 1" less than my previous prop due to the FOF blade design (per the FOF tech).
- I had several pictures of the new FOF prop installed before launch and there is over 2" of clearance.
- I have not seen any smoke of any color coming from the exhaust system
- Should I haul out and replace the new FOF prop anyways?
* As noted, I notice some virbration when motoring upon splash and traveling to my marina. I assume it was just the typical 2 blade prop vibration, as my other prop had some but not as much. I wondering if perpaps my shaft alignment is off and the folding prop vs the fixed enchanced this more. *** Realign my shaft? When the RPM picks up, it is causing the shaft to not spin properly.... Process seems fairly straight forward (my last words)

Exhaust, Cable and Etc..
- Exhaust elbow looked clean. I was going to remove the hose and other areas to double check.
- Throttle cable extends out properly - no binding and obstructions

I am quickly running out of troubleshooting thoughts.

 

[Christian Williams]

Frustrating. When the RPM picks up, what does the shaft do ("it is causing the shaft to not spin properly")?

I would probably go under the boat and grab the cutlass bearing flange and try to confirm it is secure. Also take a look at the motor mounts, they can break and disturb shaft alignment.

 

[Pete the Cat]

Thanks for all the replies and input. I know this thread is going on longer than it should but it has been helpful to bounce troubleshooting concepts off of everyone and I really appreciate it.

I created a list of what has been done and what possibly could be researched.
Fuel Delivery System:
Completed Tasks
- All fuel hoses have been replaced and associated clamps and fittings from the fuel tank to the injector pump. System seems tight.
- Bleed valve was removed, cleaned and reinstalled with the knob tight to the nut.
- Replaced the old Racor fuel filter assembly with a 500 series. (note: one of the extremely difficult process of finding a air leak last year was in my older Racor alum bracket. When I removed it completely, I saw a hairline crack on the backside).
- Removed, cleaned and replace the screen in the round Gold fuel lift pump.
- Removed all fuel, whip tank bottom clean and added fresh fuel for spring
- All new fuel filters
Not done
- Replaced fuel lift pump? seemed okay and provides pressure. Engine does not start hard.
- Service fuel injector pump and injectors? I was going to wait until the winter, while the sailboat is on the hard
- I have nothing else on the fuel side

Propeller and Etc...
- New cutless bearing and stuffing box (repacking) was replaced 3 yrs ago and appears to be in good condition
- New prop was installed during the winter; the prop is a 2 blade 15x10 FOF and my previous prop was the standard 2 blade fix 15x11.
- 1" pitch equals +/-200 rpm, and having a max RPM of 2000 to 2100 with a clean bottom and prop, that does not sound like that is the issue. The prop pitch would have been 3" to 4" off. Also it has 1" less than my previous prop due to the FOF blade design (per the FOF tech).
- I had several pictures of the new FOF prop installed before launch and there is over 2" of clearance.
- I have not seen any smoke of any color coming from the exhaust system
- Should I haul out and replace the new FOF prop anyways?
* As noted, I notice some virbration when motoring upon splash and traveling to my marina. I assume it was just the typical 2 blade prop vibration, as my other prop had some but not as much. I wondering if perpaps my shaft alignment is off and the folding prop vs the fixed enchanced this more. *** Realign my shaft? When the RPM picks up, it is causing the shaft to not spin properly.... Process seems fairly straight forward (my last words)

Exhaust, Cable and Etc..
- Exhaust elbow looked clean. I was going to remove the hose and other areas to double check.
- Throttle cable extends out properly - no binding and obstructions

I am quickly running out of troubleshooting thoughts.

I had a situation similar to this on a friend's boat. Please do not ask me to explain how this could be, I am still scratching my head: He did have black smoke when he tried to go to full power so that is different. But he could not get his engine to develop full power under load--suddenly. But he went through everything as you did and finally found out the exhaust manifold was blocked. This was a new engine with less than 400 hours on it. He went through the whole fuel system (filters, injector pump tested and serviced, new injectors, and new exhaust elbow--and it still would not develop full power). Cleaned exhaust manifold (it was visibly clogged) and now runs like a top. He claimed the problem suddenly appeared and that he had not excessively idled the engine. I have no idea how this could occur but it is a real example.
Here are two more options if that does not work:
1. Is it possible that the yard bent the shaft when pulling and splashing the boat? This should be obvious from vibration, but that could hiccup the engine so that it does not develop full power under load. Bent shaft or significantly out of line engine can cause these symptoms. You should feel vibration as it approaches the max RPM it will turn under load, however.
2. Prop folks made a mistake with the dial when they bent the prop for pitch? I have seen it happen. You had proposed a short haul and installing the old prop. This would confirm the prop pitch was or was not the issue and could document the yard bending the shaft if that is causing it (happens more often than you would think--when the lift guys do not tie the straps together because they are sloppy and they slip out on the shaft). You would want to be there when they haul.
Those are my thoughts at this point based on my understanding of the situation.

 

[Kenneth K]

I am quickly running out of troubleshooting thoughts.

Have you checked the length of the 1-5/8" exhaust hose from exhaust elbow to thru-hull? Any kinks? A blockage in the water-lift muffler (not hard to remove and clean out)? A funny brass-plumbing-type check valve installed between engine and muffler (could be blocked/stuck)? Is there a Marelon valve located at the exhaust through-hull (are you sure it's fully open)?

 

[Loren Beach]

I wonder if the actual exhaust hose is original to the boat? When I replaced our engine in 2018, one of the (minor) reasons on my long list of accumulated woes was a section of the OEM exhaust hose that was seeping rusty water. i.e. the multi layer hose was failing to contain the water & exhaust.
Also, a friend with an '82 Ericson 33, had to replace his original exhaust hose about a decade prior when the sound changed from the water and gasses being pushed out. Turned out that the old hose had an "aneurism" inside where the inner layer(s) had opened up and there was an on-and-off partial blockage of the hose interior.
Just my opinion, but.... for all of our 1980's models, this is one more part that simply wears out from age. If your boat still has the original exhaust hose, it is probably time to replace it.

 

[patrscoe]

I am going to run the sailboat at various RPM and video tape the shaft to see if there is a greater vibration and movement at higher RPMs. If nothing seems out of the normal spinning of the shaft, I will have the boatyard perform a short haul and I will replace the prop with the fixed 2 blade prop.
Yes, where I put the sailboat on the hard, which is a different marina vs where my slip is located, could have mis-handled the lifting of the sailboat.

I am going to see if I can dismantle the exhaust and go through the system and replace hoses, clamps, fittings, etc.. what I can and a good cleaning as necessary. Check for any partial blockage throughout.

Going to review the fuel delivery system again, check my hoses and connections, check the fuel vent, replace the fuel lift pump which I ordered earlier this week... I don't think this is the cause but I will go through it again.

I am starting to look at this differently and thinking it is not one major issue but multiple minor issues. Perhaps the new prop is causing too much vibration or I have a shaft alignment issue which is making the folding prop react differently losing 200 to 300 rpm, carbon build up in the exhaust system - another 200 - 300 rpm (as I have been running the motor under 2000 rpm for a while now, especially the last 2 yrs searching for air in my fuel system and lack of performance from the injectors/injector pump as they look like they are original... another 200 or so rpm.
It's not like I am working with a 5 yr old diesel engine - It's 34 yrs old.

 

[gryf]

The governor is a set of spinning weights deep in the engine. You do not want to go there. I seriously doubt if this is the problem. I agree with you that you should hope that it is the exhaust elbow (or manifold). On my installation the Elbow is an Onan part you can find on EBay--and there are people who will fabricate something from SS that will be cheaper and better than the OEM, but yours might be different. They are sometimes impossible to clean and need replacement. For folks thinking about prop replacement: adjustable pitch is expensive but often cheaper in the long run than the alternative things you have to do to adjust pitch (haul boat, remove prop, repitch, relaunch, repeat). The fixed two blade that came with my Ericson is properly pitched (my experience is that production boats are often over pitched). I have an Autostream feathering prop on my Tartan that I have had for 20 years that is externally adjustable and has been a dream--a very good investment and I have been able to adjust it by free diving it.

I actually had a very similar problem on my Ericson 30+ with the 2 cylinder 16HP Universal. After inspecting all of the usual items such as fuel, fuel pump, injector pump, exhaust elbow, fuel tank vent, etc it turned out to be the spring which is part of the governor assembly. After replacing the tired spring the engine is able to maintain the correct power and RPMs regardless of the load. I would highly recommend inspecting this as it also took me over a year to isolate the issue.

 

[Pete the Cat]

I actually had a very similar problem on my Ericson 30+ with the 2 cylinder 16HP Universal. After inspecting all of the usual items such as fuel, fuel pump, injector pump, exhaust elbow, fuel tank vent, etc it turned out to be the spring which is part of the governor assembly. After replacing the tired spring the engine is able to maintain the correct power and RPMs regardless of the load. I would highly recommend inspecting this as it also took me over a year to isolate the issue.

Despite my original advice, I think this may be the possible problem now that you have eliminated the exhaust elbow and if you are confident of no other obstruction in exhaust. As I recall, this governor spring is going to be hard to access on a 25XP, but the point is well taken that if you have done all the easy stuff, this could be it. I have done enough of this work to never be certain of my diagnosis--even when the thing magically starts working again.
We are not doing much to target your problem. Remember Occam's Razor. What was changed when this problem started?

 

[Christian Williams]

Yes, I would try the prop change test. It's the simplest and you need to absolutely eliminate the most likely cause.

 

[patrscoe]

I think I am going to complete list above and rule out all I can and yup, replacing the prop is one of them.
If all else fails, I will look at the Governor spring.