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Old 08-10-2014, 11:04   #1
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Falling short of max engine RPMs

Our boat has a westerbeke 21 in it, and according to the manual, this engine should turn 3k RPMs. Underway our boat will only come up to about 2400 RPMs, and even with no load on the engine will only come up to 2700 RPMs.

I plan on getting a hand held Tach to make sure the boats tach is reading correctly. Aside from that, what other things can keep a diesel engine from coming up to Speed properly?
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Old 08-10-2014, 11:18   #2
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Re: Falling short of max engine RPMs

Prop pitch. 2400 max under power might be a little low, but I wouldn't worry about getting to 3000 under power.
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Old 08-10-2014, 11:29   #3
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Re: Falling short of max engine RPMs

I wasn't too worried about getting 3k while underway, but even with the trans in neutral and the batteries fully charged, she'll still only turn 2700.

There's no black smoke that I've been able to detect under any rpm or load, and one website I read leads me to believe this is probably a fuel delivery issue then, possibly old fuel filters. We did just aquire the boat, so I have no idea when they were replaced last. The boat has twin RACORs and one appears to not have ever been used as there's no fuel in the bowl, so I can switch that easy enough. The fuel filter on the engine is still in place too, so I think I'll replace that as well.

Sound reasonable? Any other ideas? I know our air intake box is cracked pretty bad bc someone over tightened the fasteners and crushed the side in slightly. Not sure if this could be restricting air flow and causing problems.
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Old 08-10-2014, 12:20   #4
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Re: Falling short of max engine RPMs

Pretty sure it's not a fuel restriction thing, reason is out of gear it doesn't take much fuel to rev to 3000.
Before you do anything, check the tach. Of course changing the filter can't hurt if nothing else you then know how old it is.
Fuel restrictions usually almost always show up as it runs full throttle fine for a few seconds, then bogs down
If the tach is good, then look to see if there is an exhaust restriction

If that's not restricted, maybe the governor is just turned down, or maybe your throttle cable isn't opening the fuel control fully, running out of cable before the fuel control hits it's stops?
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Old 08-10-2014, 13:03   #5
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Re: Falling short of max engine RPMs

yea, I'll definitely check the tach for accuracy first.

When we were bringing the boat home after we took delivery, at one point in time the engine did lose about 300 rpms for maybe 10 seconds. Afterwards, it came back up to 2400 (which is what it was running before hand).

I thought about the throttle linkage being out of adjustment, so we verified that it is hitting the hard stop at WOT. No idea about the governor though, diesels are pretty new to me, so I'll have to look into that one. I'll check the exhaust too, not sure where the restriction would be. The water inlet for the exhast is shortly after the manifold, and it pumps plenty of water.
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Old 08-10-2014, 13:28   #6
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Re: Falling short of max engine RPMs

It doesn't sound that far off. Maybe it's just how somebody set up the boats Prop pitch and gov settings? 2400 seems a little low, does it blubber and smoke when you add more power above 2400?
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Old 08-10-2014, 13:54   #7
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Re: Falling short of max engine RPMs

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Originally Posted by blinkerfluid View Post
I'll check the exhaust too, not sure where the restriction would be. The water inlet for the exhast is shortly after the manifold, and it pumps plenty of water.
The exhaust elbow that mixes water and exhaust is what can plug up with carbon and cause a restriction. There was a thread on here about it not too long ago. I'll try to look for it. The elbow is actually considered a regular maintenance item and is supposed to be replaced every so often.
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Old 08-10-2014, 13:57   #8
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Re: Falling short of max engine RPMs

Here's the thread. It has some good info about the exhaust side of diesels for you to become familiar with.

Yanmar Maintenance issue: Mixing Elbow
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Old 08-10-2014, 14:38   #9
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Re: Falling short of max engine RPMs

No blubbering or smoke at any RPMs.. though it doesn't seem to have the strongest idle, always sounds like it's going to stall if I put it in gear and leave the engine at idle (though it hasn't stalled yet).

I'll definitely be sure to check out the exhaust elbow. I know I read in the log books that one of the previous owners had replaced the elbow, though I don't remember when, somewhere around 7-10 years ago, so it may be due again.
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Old 08-10-2014, 16:12   #10
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Re: Falling short of max engine RPMs

Hi OP,

An accurate description of all running events is quite useful as opposed to dribs and drabs of occurances.

That said,a64pilot,gave valid proposals to look into.Some govenor system probably holding back Max rpm.Though that RPM dropout you mentioned after inicial post is concerning.
So, I would consider further,new fuel,filters,mechanical(govenor,throttle cable adjustment...) With the additional of an injector cleaner added to the fuel.Now,this will create accrid odor so don't fret.Run engine(s) up to steady state temp then-Run the through and when really accrid exhaust odor(injector cleaner) - work throttles to max then down repeatidly-this'll bring your injector tips back to as best you'll get short of changing them out(the tips).Sometimes takes awhile for injector cleaner to work so be patient-it'll come along.They may be damaged from prolonged period out of use.Just buy new tips if this is the case.



All the Best
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Old 09-10-2014, 09:16   #11
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Re: Falling short of max engine RPMs

is the engine getting enough air, filters etc
Ross
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Old 09-10-2014, 10:17   #12
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Re: Falling short of max engine RPMs

Change all your filters just so you know. Tag them with date and engine hours. A diesel is a pretty simple devise. If it runs at all I would look at fuel last, check your breather first it's the simplest, and the exhaust for carbon next. You know your not over wheeled or at least that is not causing it. It sounds like you shouldn't even dick with the governor. I think someone suggested the former owner may have done that.
Ask them if they did. Good luck, it don't sound major.
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Old 09-10-2014, 11:25   #13
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Re: Falling short of max engine RPMs

Quote:
Originally Posted by a64pilot View Post
Pretty sure it's not a fuel restriction thing, reason is out of gear it doesn't take much fuel to rev to 3000.
Before you do anything, check the tach. Of course changing the filter can't hurt if nothing else you then know how old it is.
Fuel restrictions usually almost always show up as it runs full throttle fine for a few seconds, then bogs down
If the tach is good, then look to see if there is an exhaust restriction

If that's not restricted, maybe the governor is just turned down, or maybe your throttle cable isn't opening the fuel control fully, running out of cable before the fuel control hits it's stops?
Quote:
Originally Posted by ontherocks83 View Post
The exhaust elbow that mixes water and exhaust is what can plug up with carbon and cause a restriction. There was a thread on here about it not too long ago. I'll try to look for it. The elbow is actually considered a regular maintenance item and is supposed to be replaced every so often.
Quote:
Originally Posted by rmw2007 View Post
is the engine getting enough air, filters etc
Ross
Good posts!

The temporary RPM drop you once experienced could have simply been something like a plastic bag on the prop. So don't over-complicate your analysis. Since you can't achieve full RPM, in neutral, prop pitch has nothing to do with it (though you still might be over-propped).

Make sure you are reading the manual's RPM data correctly for your precise year/model. Calibrate the tach, first, so you know, for certain, what the RPM actually is, since this is what first made you concerned.

Make sure the intake and exhaust aren't restricted.

How old is the fuel? Diesel loses its potency over time--its cetane rating drops. Check fuel system thoroughly.
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Old 09-10-2014, 11:44   #14
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Re: Falling short of max engine RPMs

You're getting good advice. Old fuel is one that catches me every once in a while.

I had a W27 that had a really badly calibrated tach. A laser tach is cheap and the adjustment (screw on the back) was easy.

My W27 had two on-engine fuel filters and the second one (hidden in side the fuel pump) had never been changed. It was still painted shut with red paint from the factory 2700 hours and 30 years before I changed it!
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Old 09-10-2014, 12:06   #15
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Re: Falling short of max engine RPMs

Is your engine compartment sealed up really well? The reason I ask is that a lot of them are sealed better than one would think. Or well enough anyway, that the engine doesn't get enough air when it's under higher loads.
And of course it goes without saying, to make sure that there's naught in the air filter overly restricting the flow. This is a SWAG, but you could try running it for a minute sans filter, & see if she performs better.

Also, it may be covered in that link about exhaust issues. But running an engine with some regularity, just to charge the batteries (at low rpm), can cause carbon buildup in the exhaust elbow/manifold. Which is easy enough to check.
That, & make sure that there aren't any sharp kinks in your exhaust hose. Also, each elbow in an exhaust or cooling system adds a huge amount of restriction. Much more than one would think anyway.
I forget the numbers exactly, but I want to say that each extra elbow is akin to adding 10' of hose. It's just a thought. One I learned the hard way.
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