Black smoke @ high revs

[NUTMEG]

Eve all. Just been reading the latest installment of Dylans posts. My problem seems tiny by comparison.

The last two trips out we have had to motor back (foul winds and tides) on both occasions I thought it would be a good idea to open up the little 1GM10 to give it a good clear out for 15 minutes or so. Usually she does little more than tickover in and out of the marina.

After 10 minutes or so of running at max throttle I noticed clouds of black smoke issuing from the exhaust. Also black carbon deposits in the exhaust water. I am sure this is unburnt/poorly combusted diesel as no oil is being consumed and I would expect the smoke to be 'bluish' if it were engine oil.

The engine starts and runs perfectly, no funny noises or any sign of overheating. If throttled back to cruising speed (maybe 1/2 to 3/4 throttle) the black smoke stops and the exhaust water runs clear again.

So I suspect the injector is in need of a service, am I right in thinking worn needle seat/weak return spring could be the problem? Any opinions would as always be very welcome. Thanks.

 

[Richard D]

Black smoke

Most likely is that as you only potter about in the marina and this is the first time you gave opened it up, the smoke and dirt is just accumulation of exhaust grim over a long period and will clear with more running, or could be a sign oif a blocked air filter.

Richard

 

[Spyro]

Maybe not so serious. A dirty hull or prop can overload a small engine very easily. Black smoke could be caused by unburnt diesel

 

[penfold]

If the points Spyro mention aren't the problem, it could also be a choked exhaust; corrosion in the water injector elbow or delaminated/collapsed rubber hose. Also check the airfilter if any is fitted; how airtight is your engine compartment? Some are terrible and have inadequate air inlets. Also possible is too large/overpitched propellor; has the prop been changed recently?

 

[mitiempo]

Does it run cleanly at high revs in neutral? If so I would bet it is the exhaust elbow that is restricted - very common and exactly the symptoms you describe.
Engines need to breathe in and out.

 

[NUTMEG]

Thanks

Some ideas that I would not have thought about.
No air filter, so not that
Plenty of air into engine compartment
Lots of trailing weed- will sort that next week
Could have barnies on the prop- they seem to like it, will check
Exhaust elbow was fine last August- will whip it off and check

Thanks again, what a great resource this place is!

 

[steve28]

also the prop could be have growth on it or be slightly over pitched.

Steve

 

[sarabande]

the exhaust system could be carboned up from lots of low running, and this high speed burst could be clearing it out ?

 

[Tranona]

Too much low speed running. Exhaust elbow probably needs a proper clean - and the exhaust port. These engines need to run hard. You are not doing it any favours by just pottering in and out then shutting down. The raw water cooling means it takes some time to get up to full operating temperature. Yanmar recommendation is to run it a full revs periodically, so next time you go out, give it at least 30 minutes flat out. Almost certain you will find the black smoke etc disappears - unless of course you are overpropped and it is not able to reach full revs (at least 3400)

 

[jakeroyd]

I get a similar but not so serious amount of black smoke out of my 1GM10 when near to flat out. I have removed the elbow which was clear.
It has had several long runs recently , about 5hrs running at say 80% throttle and it still black smokes a bit. I reckon this must be the equivalent of what the Yanmar manual reccomends.
This I think also keeps the bores unglazed as well as stopping the exhaust coking up.
I've stopped worrying about it unless it gets worse.
Almost flat out I get some black smoke and some oily water out but not agreat deal , enough to make me throttle back a bit.

Starts and runs fine and always has.

Gives you a sense of proportion for your engine ?

 

[NUTMEG]

Thankyou,

When smoking there is such thick black smoke that you can only just see the exhaust outlet looking over the transom, a distance of maybe 3 feet or so. it reminded me of that Jaws film when the crusty old fisherman was pushing his boat to hard and blew the engine. No Great Whites up the Blackwater though.

 

[Tranona]

When smoking there is such thick black smoke that you can only just see the exhaust outlet looking over the transom, a distance of maybe 3 feet or so. it reminded me of that Jaws film when the crusty old fisherman was pushing his boat to hard and blew the engine. No Great Whites up the Blackwater though.

Symptoms of fouled or over pitched prop. You need to get a rev counter on it to see if it is reaching full revs. With such limited power from the engine - even on a small boat - getting the prop size right is critical. Just 1" difference on pitch can affect running by 300 revs - roughly 10% of its power output.

 

[angelsson]

Maybe not so serious. A dirty hull or prop can overload a small engine very easily. Black smoke could be caused by unburnt diesel

Would suggest the same, particularly the prop being encrusted.

 

[NUTMEG]

Good idea

The prop, as far as I know, is original, never noticed heavy smoking before. I know there is a fair bit of weed around the waterline, and at last years lift the prop looked like a barnacle farm. So, wetsuit on and wire brush the prop I reckon. thanks chaps, will report back when I have evicted the crustaceans!

 

[hurley]

would definitely agree with earlier replies. Important not to underestimate the effect of fouling to the hull and prop, even a few barnacles on prop can have effect .