Calling all Yanmar Gurus...

[kloudie1]

No smoke through RPM range says injectors are probably OK and you are left with an overload .. The prime suspects are: too much prop pitch or a clogged exhaust ell. The clogged ell will cause a power decrease leading to an overload where there shouldn't be one. You can probably read the prop pitch by sanding the hub lightly with waterproof sand paper (without pulling the boat). Happy hunting!
Benny is correct about a "tune up" ya really should verify that the valve clearance is OK while you are messing around in there.

 

[fredr]

As folks have correctly stated, the engine is over loaded. (black Smoke)
If you are certain that the prop shaft is turning free, the prop and shaft are clean, and the bottom is clean then...
Black smoke at max throttle and only 4.5 knots = over size prop or the alternator or raw water pump or... is loading the engine. It is a good idea to check the air intake and the exhaust elbow.
It could also be caused by the engine having low compression and not making full power, the governor is trying to get the engine to max throttle by giving it more fuel = black smoke. When under way at max throttle, you can check for blow by coming from the crank case vent at the valve cover. This would be the combustion gases getting past the piston rings and causing a loss of power. More often Yanmar's have combustion gases leaking past the valves.
You can elliminate the black smoke with an adjustment but that does not cure the issue of low boat speed. You need to find the RPM at max throttle UNDER WAY.
You could use a manual hand tach on the front engine crank IF YOU ARE VERY CAREFUL not to get caught in the rotating parts.

 

[Scott T-Bird]

Yes, definitely check for blow-by. The symptoms I had with loss of power, speed and increased black smoke at WOT included significantly increased blow-by. You can check by removing the dip stick or the oil cap while running the engine and hold your hand over the opening (be careful of moving parts). If you feel bursts of air, the blow-by indicates loss of compression and possibly worn rings.

 

[BobM]

In NC? Have you gone for a swim yet?

 

[Chris Patterson]

Lake Norman is still pretty cool to be swimming in yet.

And it sounds like that area good use some decent mechanics. You know, boat mechanics. That know how to work on boats. Truly you need to find one of these..

 

[petersea]

All very good suggestions so far just let me chime in that as far as the elbow getting clogged that is a salt water issue so unless you boat was in salt water prior most likely not the problem but check it any way and replace depending on condition. Get the fuel filter thing fixed first and check. Don't do too much as one time with out doing a test run to verify the repair was done correctly and not chasing a problem that was not there before. The big question here is did the problem exist be for the mechanic did the other repairs Unfortunately if you don't know now you need to chase down all possibilities. Ask the original guy that did the work to come on a test ride with you. Maybe he can find something,even the best mechanic can have a bad day. May want to consider adding some fuel treatment to fuel if your filter is as bad as you say, the "black nastiness" is probably algae. First thing I would do is get the fuel issue corrected, diesels need clean fuel to run correctly. May also want to consider diving under boat again and doing a "visual and hands on" check of shaft and prop, check rudder also, the hard to port at more then 3/4 throttle is strange and not sure how it could be tied to engine performance or even the alignment. While a lot of boats have some push do to prop thrust your description seams excessive. Is there another similar boat you could test and compare yours to ?? Hull speed should be a little over 6 knots so your speed is down as you should be close to hull speed at WOT. What are you using to measure speed and is it accurate ?? And are you sure you are getting WOT spec rpm ? with out a working tach it is hard to tell. Good Luck and keep us updated on what you needed to do to fix.

 

[Maine Sail]

#1 Before anything else, is to get a digital photo tach and measure MAX RPM at WOT..... Until you know your engine can turn max rated RPM everything else is secondary.. Your symptoms are indicative of being over propped...

#2 How are you confirming STW. Speed through water?

 

[puddlejockey]

Updates!

Guys, thanks for the phenominal advice.
As an update, I'm replacing the enitire fuel filter assembly and fuel line with a newer unit,

Checked the inflow of water and replaced the impeller ....impeller looked good, but I was there anyway.

Exhaust elbow ( although I already have one on order) was probably 80% clear! just a layer of carbon as I'd expect.

The fun part is, I pulled the flexible portion of the exhaust hose to check it for interior degradation....and there was about 2 ounces of jet black oil laying in the hose...
The exhaust port and head are heavily carboned, but since that's subjective, and I can't get a very good angle to look, I'm don't know if what I see is normal.

I'm on the 5 week waiting list for mechanic #2 , New tech on the lake, but I got a good feeling from the guy, and his work is warranted.
Valve leaking? Bad rings? The universe telling me I need an alerion 28?

****. I was thinking of selling her prior to this adventure, and decided not to since she's in better shape overall than any sub 20k boat I've seen around here. Sadly, since I overdid replacing and upgrading almost every working component so far, ( winches, lights, bottom paint, interior , paint, running rigging) , I'm already about 14 into what's probably an 8500.00 boat in this market.

Grrr....

 

[Scott T-Bird]

I know that feeling ... but what else are ya gonna do when ya want what ya want.

 

[puddlejockey]

Actually, our first swim of the year was Memorial Day, with about 74 degree water temps! By now, with our current 5 consecutive 90 days, the upper thermocline is Inthe low 80's.

The boat ran much better than it was running, post fuel filter assembly replace and exhaust elbow clean out, so I regret doing neither.
That said, hitting WOT is still like pressing the " smoke screen" button while in gear. Thinking of labeling it as such.
Engine starts great, runs smooth, and will run up neutral without a puff.

I checked with the mechanic/ yard that did all the work last year, per them the prop was the correct size and pich, and in good shape.
Currently seeking diver volunteers to take a closer look.

What am I missing? Possible for something In the gearbox itself to be creating drag on the motor? Could it be a fuel mixture issue that doesn't show itself until WOT?
All in know is I have to figure it out in time to cancel( or keep) my place on the mechanics waiting list, and I now it's going to big the hell outta me..

 

[Maine Sail]

Actually, our first swim of the year was Memorial Day, with about 74 degree water temps! By now, with our current 5 consecutive 90 days, the upper thermocline is Inthe low 80's.

The boat ran much better than it was running, post fuel filter assembly replace and exhaust elbow clean out, so I regret doing neither.
That said, hitting WOT is still like pressing the " smoke screen" button while in gear. Thinking of labeling it as such.
Engine starts great, runs smooth, and will run up neutral without a puff.

I checked with the mechanic/ yard that did all the work last year, per them the prop was the correct size and pich, and in good shape.
Currently seeking diver volunteers to take a closer look.

What am I missing? Possible for something In the gearbox itself to be creating drag on the motor? Could it be a fuel mixture issue that doesn't show itself until WOT?
All in know is I have to figure it out in time to cancel( or keep) my place on the mechanics waiting list, and I now it's going to big the hell outta me..

You are missing an actual RPM reading at WOT.. Spend the $30.00 on a digital photo tach and confirm neutral and loaded WOT... Over propping is not uncommon but should be corrected...

 

[Chris Patterson]

But did you change that filter yet?..
I would do that.

 

[puddlejockey]

Thanks, all.
Chris,filter replaced..actually whole new rancor filter/ water separator.
Next step, as others have said, will be to check RPMS as soon as I can secure a willing copilot....

 

[seadaddler]

Mixing Elbo

You said the mixing elbo was clean but just wondering
if you took it apart the 2 pieces apart and look inside.
Nick

 

[puddlejockey]

Sea, the mixing elbow is one piece cast steel , or at least there aren't any nuts/ bolts to split the halves. It was clear, but certainly not clean , probably 1/16th of an inch of carbon buildup. I have a new one on order, as this one seems to be factory, JIC..

Interestingly, I found an old thread from 2011 with someone asking the exact same questions, with the exact same issues, on an " ask questions" general forum. I may see if there is a way to follow up with the op and hear his or her solution..

 

[DougM]

You mentioned that you changed the RACOR filter. What about the secondary filter on the front of the engine? Has that been changed?

 

[puddlejockey]

Doug,
I would never admit that I completely overlooked the filter on the motor itself. That said, I think I'll make a quick run down to the boat.......

 

[puddlejockey]

Hi All!
Just a follow up FYI; it's a "good news/ bad news" situation.

The VERY GOOD news is that it looks like the fuel injector isn't atomizing properly and/ or the valves just need to be adjusted. It turns out that if you increase the throttle quickly in neutral you can produce the same result.
When I was trying it in the slip, I was easing the throttle up. The mechanic believes that the "slow" increase in throttle gives it time to build up enough pressure to burn the fuel, but that the "quick" push doesn't. Under load, the drag on the motor of being underway doesn't allow for the RPM's to build enough for the above.

The BAD news is that I'm having the work done, then selling her anyway. Damn. When we bought her, I did all the "expensive" stuff, all the critical repairs, then went waaay overboard with upgrades. Oh well, welcome to boating...

 

[RichH]

The OP signs and symptoms are commonly caused by:

1. Throttle decreasing all by itself - tighten up the clamping friction nuts (inside the binacle or behind the bulkhead where the throttle is mounted).

2. Most sailboats are 'over-propped' meaning their pitch is too great, especially near WOT.
You do want some wee bit of over-propping at your cruising rpm as the wee bit of excess excess fuel will help to cool the combustion chambers. If you dont have any smoke at the high end of the cruising rpm, leave it alone; if you do have a lot of soot on your transom after long periods of cruising; then, have the injectors checked, the injection pump checked, and/or change the prop pitch

3. Thats prop-walk -- it means that the tips of the propeller are coming too close to the hull. All props will have such prop walk in forward (or reverse); if this is severe, it suggests a change to a 'less pointy' blade shaped prop or a prop with less diameter. Most folks simply 'live' with such forward at speed 'prop walk' - its considered normal if its not 'severe'.