Black smoke from Yanmar 3GM

[jimi]

When I revv hard I get a lot of black smoke initially (fot 2 to 3 secs) and a sooty oily deposit comes out the exhaust. It then disappears. If I increase revs slowly I don'nt get it. What might be causing it?

Out of interest I finally tracked my starting problem down to a slightly twisted seal on the primary fuel filter.

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[vyv_cox]

I find that partially burnt oil accumulates somewhere in the exhaust system if the engine has not been run hard. If I run at maximum revs for about 10 minutes, all this stuff is burnt up, oily smoke emitted at first, then everything clears up. It is then OK for a few months. This is a well-known "cure" by engine specialists who will charge you 100GBP for the privilege.

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[DepSol]

Lack of oxygen under load as the fuel comes rushing in the air takes a sec or two to catch up on the mixture. Ie the stoichiometric ratio is not balanced. Not a problem really. You could try Soltron if you havent already as it allows the fuel to burn at a lower oxygen ration. Or try putting a new air filter in.


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Now where is that Brendan hiding?

 

[brianhumber]

Do not open the throttle quickly. Marine engines are generally simple in design and opening the throttle wide thus putting max fuel in before the engine is running fast enough to get enough air in it just means unburnt fuel ( black smoke) in the exhaust. Look at a ferry's stacks 15 mins before it leaves as the engines are put on load for example.
Blue smoke is lube oil derived and the HST Paxman engine's smoke as they leave a terminus is a good example of this.

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[brianhumber]

Do not open the throttle quickly. Marine engines are generally simple in design and opening the throttle wide thus putting max fuel in before the engine is running fast enough to get enough air in it just means unburnt fuel ( black smoke) in the exhaust. Look at a ferry's stacks 15 mins before it leaves as the engines are put on load for example.
Blue smoke is lube oil derived and the HST Paxman engine's smoke as they leave a terminus is a good example of this.

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[ParaHandy]

You might get the answer here .... I've set the URL search engine up with black+smoke+exhaust. It's the USA Yanmar engine forum....

http://forums.torresen.com/eThreads/view/engines/search?query=black+smoke+exhaust

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[Birdseye]

Mine does exactly the same. Unlike your car, your boat has a simple mechanical fuel injection system - open the throttle and more fuel is injected proportional to how wide you've opened it. But the air intake is related simply to engine revs, so until the revs rise sufficiently you have too much fuel for the air. Result, solid carbon is blown out rather than carbon dioxide.

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[Heckler]

black smoke is caused by partially burned diesel, when you open the throttle fully on a diesel engine it tells the governor to open the pump rack fully, the pump delivers maximum fuel and until the engine revs increase enough to suck in enough air to combust the excess fuel completely it will throw out partially combusted fuel ie black smoke. this is normal, (as the revs build the governor starts to control by shutting the fuel supply down)
turbo charged engines are worse in this respect because they are waiting for the turbo to spool up as well to push enough air in to give complete combustion.
sophisticated diesels have clever governors that "limit" the flow of fuel while the revs are building to avoid this phenominum.
if there is unburned lube oil in the exhaust it will burn with a white smoke if you do what coxy is suggesting, i would certainly not run the engine at maximum speed for ten minutes unloaded especially if it is one of the ones with a timing belt on.
stu

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[vyv_cox]

Sorry if I misled you. I meant full throttle under load. I know of several yards who do this.

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[Heckler]

i thought whats going on, usually you are so meticulous about what you say.
stu

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