2000 Yanmar 3GM30F Black Smoke and no power

Sep 26, 2008
546
Hunter 340 0 Wickford, RI
Yesteday everything was great....fast forward to today and my 2000 Yanmar 3GM30F is spewing Black Smoke and I can't get any RPM's over 1000.
It starts up just fine but now Black Smoke and no power.

I check the fuel filters ( replaced last year) and they look fine. Tank is just under 3/4 full.
Fuel flows easy enough, no gunk, water or contaminants you can see.

Impellor is good (new this April). Water is clear from intake to exhaust.
I checked the air filter and while it's not new it' s clean. And I ran it without the filter and still same problem.

But there is no power above 1000 rpm in neutral, forward or reverse.

I'm thinking Injectors ?? It just feels like it's starving for fuel. The engine has 387 hours, all mine, as I purchased the 340 new in 2000.

Any ideas or similar events to others, and where I go from here?

Thanks for the help.
 
Last edited:
Nov 6, 2006
9,884
Hunter 34 Mandeville Louisiana
Usually black thick smoke is too much fuel.. If something is causing the motor to not have enough power to get to RPM, the governor will increase fuel quantity to try to make more power.. black smoke says ya have too much fuel in the cylinder.. fouled prop is generally the thing to suspect if it changes suddenly..
 
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Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Yes. Sudden onset suggests leaking injector. Also did you check mixing elbow for debris/occlusions particularly if you have a swan neck version.

Charles
 
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Sep 26, 2008
546
Hunter 340 0 Wickford, RI
Kloudie1 and Charles,
I haven't checked the mixing elbow or the prop yet. The prop turns in both forward and reverse and really doesn't "feel" like it is obstructed. I'll have to jump in and see what I can see there.
The exhaust looks and sounds the same as it ever did but again anything is possible at this point.
 

SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
Your prop being funky cause those symptoms. You don’t have too much load

While I think it shouldn’t be an issue. What happens at 2,000 rpm in neutral and in reverse?

I rust there is no remarkable noise or vibration? I share the view that it’s an injector or some fuel porting issues.
 
Sep 26, 2008
546
Hunter 340 0 Wickford, RI
SG,
What leads me to other causes is that it happens in neutral as well as forward and reverse.
I can't get the engine over 1200 RPM and it starts to back off on power and feels like it will stall out. The same feel and sound you get if you cover the air intake with your hand.
There are no vibrations or different noises either.
 

SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
There is a possibility of your exhaust hose collapsing (on the inside) or being bent (unlikely); you hydralift muffler being plugged-up, or elbow causing back pressure (it's the equivalent of having too little air in). You may still be seeing water coming out the stern.

If it's not the injectors or the fuel lift pump, then a compression test may be in order.
 
Sep 22, 2009
134
Hunter 36 Seattle, WA
There is a possibility of your exhaust hose collapsing (on the inside) or being bent (unlikely); you hydralift muffler being plugged-up, or elbow causing back pressure (it's the equivalent of having too little air in). You may still be seeing water coming out the stern.

If it's not the injectors or the fuel lift pump, then a compression test may be in order.
Wouldn’t the engine be overheating as well, if the exhaust system is blocked? My money’s on the injectors.
 
Nov 6, 2006
9,884
Hunter 34 Mandeville Louisiana
Yeah.. if it happens in neutral then it is definitely not a prop problem.. I read "fast forward" and had in my mind fast and forward gear.. your injector diagnosis is a good place to go look.. Happy hunting!
 

SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
Wouldn’t the engine be overheating as well, if the exhaust system is blocked? My money’s on the injectors.

Overheating? Yes, if you put the engine at (say 2800 RPM) -- but many Yanmars resist overheating at lower RPM's. Also, you could have a sudden collapse (which is still allows plenty of water to pass, but restricts the air flow.

I didn't suggest this possible cause from personal experience. But, it's one of those "after the obvious, what are other possible causes" . If the exhaust is occluded, you can have plenty of WATER, so you're cool, but block the exhaust so block proper combustion exhaust. He reported it was like the air coming in was being blocked. The blocking of the discharge air going out can also cause the same affect by backpressure. The fuel is coming in, but the combustion is incomplete. The exhaust tends to be blackish.

P.S. -- It's not so simple to figure out if you have a de-laminated exhaust hose, I'm told. The partial collapse is on the inside. Air and water still pass, they just have to keep pushing harder, and harder...

The injectors are a possibility which I'd pursue, too.
 
Sep 26, 2008
546
Hunter 340 0 Wickford, RI
I went out early this morning to try to better determine a cause.
After I started the engine, which starts right up, it idled as normal.
Once in forward or reverse gear it loses power at 1200 RPM.

But I did see the black smoke and now a black film, like soot on the water, at the discharge.
It looks almost like oil but it's not. It's a soot or dust like talcum powder on the water.

As my mixing elbow has never been changed, my next thought is the elbow is blocked. With the low engine hours (386) I never really gave it a thought.

It's really the last details I can give.
 
May 1, 2011
4,189
Pearson 37 Lusby MD
I'm with you at this point - check the mixing elbow. Had the exact same symptoms several years ago; replacing the mixing elbow solved the problem. Low engine hours are not necessarily an indicator that the mixing elbow is still in good shape.
 
Sep 26, 2008
546
Hunter 340 0 Wickford, RI
I really think that it's my first place to look. With all that's happening in these engines, to just fail like this, I'm hoping also that the elbow is the problem. It really is a large amount of water through a small area. And if the elbow inside is failing it's even smaller.

I guess I'm faced with removing it to see. Or at least the hosing from it, maybe that will show me something.
 
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SG

.
Feb 11, 2017
1,670
J/Boat J/160 Annapolis
The engine is 18 seasons old! That elbow, if it had been changed twice by now, doesn't ow you anything :^))). I hope it's that.

I believe low RPM's actually plaque-up the elbow more than more robust flow per hour of use.
 
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Sep 26, 2008
546
Hunter 340 0 Wickford, RI
SG,
I know! With all I do on the boat, replacing as needed and even before, throughout the years, I just NEVER gave the elbow a thought.
I see it, have to do things right near it, but never once did I think of it or consider replacing it. I've replaced the engine hosing, water lines etc. but for some unknown reason never gave it a thought.
I too, hope that's the issue. If so, big life lesson for me!
I'll start there then move on to the exhaust hosing this winter.

It doesn't seem like it will be that challenging a job.
I'll take some pictures as I go. Right now there isn't a heck of a lot to take pictures of.
We all got one, we all know what it is, except me I guess.
Let's hope, but it really does need to be done.
 

Sailm8

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Feb 21, 2008
1,746
Hunter 29.5 Punta Gorda
+1 on the stainless elbow on ebay if you need to replace it. Good product and fast service. I'm on my second season with mine.
 
Oct 3, 2014
261
Marlow-Hunter MH37 Lake City, MN
Have you looked at the engine stop cable to make sure it still has full travel and isn't restricted by corrosion?
 
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Sep 26, 2008
546
Hunter 340 0 Wickford, RI
I'm on my boat right now. I did check the Cable yesterday. That's fine. I've taken a few pictures I'll post.
I took the hose off the loop and found it was coated in black soot. No clogged just coated. And that's what I was seeing earlier on the water.
I am thinking of using the stainless also. As I have time to plan now.
I just started to soak the bolts with PB Blaster also.
 

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Last edited:
Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Here is a tip. Tighten very slightly before you untighten. Dont press it but see if you can.

When it goes back on you don't need to mash the fasteners either. New gasket and 15 ft lbs max is all it should take.
 
Sep 26, 2008
546
Hunter 340 0 Wickford, RI
Charles,
Thank you for the kind assistance. The bolts and the fact that I'm dealing with 18 years ( I still can't believe I'm saying that) of no movement what so ever, is call for caution for sure. I really don't want t deal with a snapped bolt right now.
I'll let the PB Balster work all night and in the morning give them a shot.

Now to buy I new one. No one here has one in stock, so time is on my side, no rush to get it off.