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Old 15-02-2010, 17:41   #1
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Yanmar 2gm20f - Black Water at 2700+ RPM

From the beginning. Motor has always ran great with regular maintenance. One day I say a large puff of black smoke and that is it. On next trip out I checked everything (oil Coolant ext..) and everything was normal. during the day it ran away on me (was not to bad but took about 8 seconds to return to idle while throttle was cut), I shut down and inspected everything but found everything was normal. On my return to the dock it ran away again with same outcome and inspection results.
Next week I came to start working on it and found the oil had come up and would pour out the dip stick hole. Coolant had not done down at all so I figured it was fuel.
Drained the oil and checked for water separation but found no separation of any type even after letting it sit overnight.
Removed and replaced the fuel supply pump, dismantled the old one just to see if the diaphragm was damaged and found nothing. I removed the injector pump and injectors and had them tested. Pump checked out and was calibrated, injectors were replaced because one was stuck open and the other was only opening partially.
I put everything back together and it tested out at the dock 100%. Even sounded better and ran smother than before. After 3 hours of testing between idle, high idle and in gear up to 1500 rpm everything was looking great. No change in oil level.
Took her out for a run, 850 rpm - 2300 rpm everything was normal. From 2300 you get throttle lag. When you move the throttle about 3/4" with no reaction. Then RPM will start to climb as normal. At 2600 RPM the exhaust water turns black. I collected some and it is full of suet particles. Not oily at all.
With no load the engine will run up to 3000 RPM with correct throttle response and clear water.
Here is all I can figure, please confirm if you think I am correct.
When removing the injector pump I did damage the 2 of the 3 shims. I could not easily get locally so I carefully flattened them and miked them to be .18 all the way around. 2 shims were .18 and 1 shim was .25. If I did not do this accurately and the damaged area was holding the pump up slightly then would this cause my problem? The pump is sending fuel a micro second late and when under a load the access fuel is being burnt. Where should I go now? Replace shims with new ones and/or look somewhere ells? Would this cause the throttle lag that never existed before?
Sorry for the long post but I appreciate any help you can offer.
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Old 15-02-2010, 17:44   #2
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Update to Post
Bottom and prop are clean. Slight fouling but nothing new that would of changed running conditions.
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Old 15-02-2010, 19:08   #3
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check your injection elbow
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Old 15-02-2010, 20:20   #4
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Quote:
Originally Posted by never monday View Post
check your injection elbow
What is the injection elbow?
If you are referring to the mixing elbow in exhaust then it has been replaced and is only a couple months old.
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Old 15-02-2010, 20:39   #5
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If it's only blowing black at full throttle you may not need to worry about it. when the engine is run at full fuel and the speed isn't up to match what the engine was designed to operate at with that level of fueling you will smoke.
On the other hand, there may be a damaged valve or lower compression caused by the dribbling injector (the one stuck open).
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Old 15-02-2010, 21:12   #6
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Given the motors prior problems NM has a valid point takes no time at all to choke an elbow under those conditions, check valve clearances and fuel timing, cheapest and easiest things first. Wot unloaded should be 3600--3800 rpm

Shakey.
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Old 15-02-2010, 21:23   #7
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If you try to push a sailboat hull past theoretical hull speed you will get smoke.

Also check that your shutdown is working properly and not hanging up.
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Old 15-02-2010, 21:32   #8
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The Mixing elbow is new.
Both Injectors are new and tested with only 4 hours on them.

I have owned this boat for 6 years. All these symptoms are new. I understand that at full throttle you will get some smoke and black water but this is happening at less than 3/4. I don't run my motor hard often but I am easily able to get 3400 RPM out of her when I needed.

If when I reinstalled the injector pump, I had a damaged shim that was holding the injector pump higher thus making it send fuel late. Would this cause fuel to be injected right after the combustion and thus the fuel would be burnt and blown in the exhaust stroke. I am told that the injector pump is very precise and that the timing must be perfect.

The biggest question that I don't understand is why would there be a lag in the throttle around half throttle?
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Old 15-02-2010, 22:37   #9
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I assume you are well under hull speed when you get the soot? At what RPM's does this start and how many rpm's do you get at hull speed? I would call a diesel wizard, tell him you need the timing / injection pump fixed and which shims he should bring.

cheers,
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Old 16-02-2010, 04:49   #10
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Quote:
Originally Posted by cfoxcvg View Post
The Mixing elbow is new.
Both Injectors are new and tested with only 4 hours on them.

I have owned this boat for 6 years. All these symptoms are new. I understand that at full throttle you will get some smoke and black water but this is happening at less than 3/4. I don't run my motor hard often but I am easily able to get 3400 RPM out of her when I needed.

If when I reinstalled the injector pump, I had a damaged shim that was holding the injector pump higher thus making it send fuel late. Would this cause fuel to be injected right after the combustion and thus the fuel would be burnt and blown in the exhaust stroke. I am told that the injector pump is very precise and that the timing must be perfect.

The biggest question that I don't understand is why would there be a lag in the throttle around half throttle?
the shim is a minor worry.
When you advance the throttle and the engine stops building RPM. You've reached the point the engine will make maximum power. This is caused from an over pitched propeller, dirty bottom, or low compression.
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Old 16-02-2010, 05:17   #11
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Replace your fuel lift pump. As you have already covered other possible causes,o utside of any potential problem with your injector pump this is the no. 1 cause of oil level increases due to fuel leaking through a ruptured diaphragm in the pump.

Note: It is possible that you have a faulty injector, even if it new.
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Old 16-02-2010, 06:48   #12
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Quote:
Originally Posted by s/v Jedi View Post
I assume you are well under hull speed when you get the soot? At what RPM's does this start and how many rpm's do you get at hull speed? I would call a diesel wizard, tell him you need the timing / injection pump fixed and which shims he should bring.

cheers,
Nick.
The black water starts at 2600 RPM. This is right after a delay in throttle response that starts at 2300 RPM where you can move the throttle about 3/4" with no repose. Then as you continue to raise the throttle RPM will once again start to climb proportionately to your input.
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Old 16-02-2010, 06:50   #13
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Quote:
Originally Posted by never monday View Post
the shim is a minor worry.
When you advance the throttle and the engine stops building RPM. You've reached the point the engine will make maximum power. This is caused from an over pitched propeller, dirty bottom, or low compression.
The RPM does not stop building it just hesitates for about 3/4" of my lever input. Then it once again begins to climb proportionately to your input.
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Old 16-02-2010, 07:02   #14
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Quote:
Originally Posted by r.furborough View Post
Replace your fuel lift pump. As you have already covered other possible causes,o utside of any potential problem with your injector pump this is the no. 1 cause of oil level increases due to fuel leaking through a ruptured diaphragm in the pump.

Note: It is possible that you have a faulty injector, even if it new.
The fuel lift pump is new and I checked it before and after the installation. It is working properly.
I will have to check but I am almost positive they tested the new injectors at my request before I took them and they were working properly. I will have to confirm.
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Old 16-02-2010, 07:09   #15
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Originally Posted by cfoxcvg View Post
The RPM does not stop building it just hesitates for about 3/4" of my lever input. Then it once again begins to climb proportionately to your input.
what's the max RPM in and out of gear?
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