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Old 25-12-2020, 13:56   #1
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Black Smoke at startup

I have a Yanmar 3GM30F with 1030 hours on it. Normally the engine starts almost immediately and has never smoked. If I'm not out sailing, I try to run the engine every month for 30 minutes. The last two times I started the engine, it took longer to start and when it finally did, it belched out a large cloud of black smoke, then settled down and ran normally.

Is this something I need to be concerned about? What might be wrong?
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Old 25-12-2020, 15:11   #2
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Re: Black Smoke at startup

Mine does it... I wouldn’t worry about it just yet. You may want to rebuild the injectors at some point. But a puff of black smoke that goes away right after start up is not an issue... I have a history with farm machinery.
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Old 25-12-2020, 16:25   #3
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Re: Black Smoke at startup

Black smoke is most likely from excess fuel being dumped into the cylinders while you are cranking when it's slow to start.
Not a big Yanmar guy, but depending on the vintage of your motor seemed to remember the 3gm30f motors as having fuel line and a check valve problem causing starting problems. Is this only since it's been cold?
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Old 25-12-2020, 16:33   #4
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Re: Black Smoke at startup

How long since you cleaned or changed the exhaust elbow. They tend to cake up and can blow some dust out with startup. That also can cause it to take longer to start.
Im not a mechanic, so only going with personal experience... but When I changed mine it cleaned up the initial exhaust and they started way easier
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Old 25-12-2020, 16:40   #5
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Re: Black Smoke at startup

Quote:
Originally Posted by chris mac View Post
How long since you cleaned or changed the exhaust elbow. They tend to cake up and can blow some dust out with startup. That also can cause it to take longer to start.
Im not a mechanic, so only going with personal experience... but When I changed mine it cleaned up the initial exhaust and they started way easier

DING DING DING— winner.

As I recall the elbow should be changed around your run hours.
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Old 26-12-2020, 10:30   #6
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Re: Black Smoke at startup

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DING DING DING— winner.

As I recall the elbow should be changed around your run hours.
Wow, really? I had 5600 hours on my 4-108 and have about 4500 on the replacement Beta. Neither has had a need for changing or cleaning out the exhaust elbow. Elbows clog up from not running engine hard enough and not hot enough. I have heard many reports of exhaust clogging but why replace the elbow if it is not rusted through? Take it off and chisel/wirebrush it clean.
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Old 26-12-2020, 11:57   #7
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Re: Black Smoke at startup

Quote:
Originally Posted by chris mac View Post
How long since you cleaned or changed the exhaust elbow. They tend to cake up and can blow some dust out with startup. That also can cause it to take longer to start.
Im not a mechanic, so only going with personal experience... but When I changed mine it cleaned up the initial exhaust and they started way easier
Good comment. Ignore it, a partially blocked elbow, and you will regret it. It is a Yanmar problem caused in part by poor design.

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Old 26-12-2020, 12:01   #8
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Re: Black Smoke at startup

As a swag, some oil if leaking down through a valve guide while sitting. If it starts and burns off, I would not be overly concerned.
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Old 26-12-2020, 12:02   #9
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Black Smoke at startup

Quote:
Originally Posted by stormalong View Post
Wow, really? I had 5600 hours on my 4-108 and have about 4500 on the replacement Beta. Neither has had a need for changing or cleaning out the exhaust elbow. Elbows clog up from not running engine hard enough and not hot enough. I have heard many reports of exhaust clogging but why replace the elbow if it is not rusted through? Take it off and chisel/wirebrush it clean.


Yea the double walled elbows are prone to wear through failure.

Perhaps a Google of Yanmar mixing elbow will provide some interesting pics

Better yet here is a link https://www.google.com/search?q=yanm...h2KmtvJ3OH3q3M
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Old 26-12-2020, 22:26   #10
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Re: Black Smoke at startup

Yes agree with checking elbow first but BillO asked an important ? Did the problem only occur once it got cold. I recommend a fair bit of throttle advance when engine is cold on yr Yammer.
Worst case scenario is ring breakages or piston probs. Search for sailorchick posts, those engines did have some problems with piston/rings but elbows is the first check with those low hrs .
If you need to replace elbow much better to go for ss option rather than Yanmars.
Start off with the simple stuff 1st.
Post how u go or have any more questions
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Old 27-12-2020, 05:24   #11
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Re: Black Smoke at startup

I think the Op needs to run his engine hard under load more.
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Old 28-12-2020, 09:46   #12
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Re: Black Smoke at startup

I have the same engine in my IP. No glow plugs so cold start is slow and I get smoke once she rumbles to life this time of year. I am in Virginia chesapeake bay country.
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Old 28-12-2020, 11:00   #13
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Re: Black Smoke at startup

Quote:
Originally Posted by dmksails View Post
I have a Yanmar 3GM30F with 1030 hours on it. Normally the engine starts almost immediately and has never smoked. If I'm not out sailing, I try to run the engine every month for 30 minutes. The last two times I started the engine, it took longer to start and when it finally did, it belched out a large cloud of black smoke, then settled down and ran normally.

Is this something I need to be concerned about? What might be wrong?
If you are running the engine every 30 minutes is it getting up to operating temperature? It takes my engines 20 minutes under load. idle speed.

I would not run it that frequently unless absolutely necessary and then only run it under load and always get up to operating temps.
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