Hi team
As l walked out to meet the owners of a boat I'm seriously looking at I was greeted by the sight of black smoke and soot from the exhaust on the water as the yanmar 20 was fired up.
The soot wasn't oily and floated. Unburnt fuel? or a pre terminal event? The owner looked surprised and I commented that is probably wasn't the best start to a pre purchase inspection ??

If it started easily and the governor was working normally, that may not be a deal breaker. I wonder if it tried to swallow something indigestible.

Not good. How long since it was last started?
It could be a sign of stuffed injectors, poor engine condition or it might just be the contents of the muffler after sitting for a long while.
How did it look after it had run for awhile and when under way?

It blew some smoke when in gear with a few revs and spinning the prop, he wasn't keen to leave the pen. It hadn't been run for a while so I'm waiting for him to have it looked at. It started first go and sounded ok. I'll wait and see what happens.

Looking at the photo again there is much more there than would come from a muffler. If his engine report comes back as ok I'd get a 2nd opinion.

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Capt_Newmo said..
Hi team
As l walked out to meet the owners of a boat I'm seriously looking at I was greeted by the sight of black smoke and soot from the exhaust on the water as the yanmar 20 was fired up.
The soot wasn't oily and floated. Unburnt fuel? or a pre terminal event? The owner looked surprised and I commented that is probably wasn't the best start to a pre purchase inspection ??

I bet he looked surprised, you showing up just as he started it. As others have said get an engine survey, but my biggest red flag would be the reluctance to take it out of the pen.
Good luck, and remember, it's a buyers market.
Cheers, Bob.

I should say that in fairness that was the first start up. There was also the claim of "it's never done that before" and the owner did look genuinely terrified by what happened.
We did a second start up about half hour later and there seemed less so maybe all is not lost.

Id be taking a fuel sample perhaps some one has added the wrong fuel . Id seen fuel tanks put diesel in a non leaded tank at a petrol station.

Injectors not clean and maybe need attention, how many hours on the engine and when was it serviced. Fuel needs to be analysed.

It is not a deal killer. If the engine has not been started for 3 months the prop will be fouled to buggery and overloading it.

Give the guy a second chance with a clean prop and run it under load in the pen till it gets up to operating temperature.

If it runs OK and the deal is right buy it and the first thing you do is get a full service done on the engine. I do that with any engine I buy be it in a boat, car or anything else.

Flat batteries, bet you the alternator is over sized and the house bank large.
It is only a 20hp engine
Charge the batteries and try it again.

That much soot is beyond a simple injector problem - I would be checking that the intake manifold hadn't swallowed something. The motor must be starved of oxygen to make that much soot. But if that was so the engine would not rev out.

The owner tells me this morning that the 90lt fuel tank has half an inch of sludge in the bottom due to lack of use. Some was sucked up and burnt off so that's what ended up on the water as soot, they ran if yesterday and the water ran clear but still with some soot. He is draining the tank, replacing all the filters and getting a mechanic to look it over.
Lets see what happens.

Disconnect the alternator belt and try it.

im with cisco on this ,every thing in the water is soot and probably built up in the exhaust from excessive idling and not using the engine at load.run the engine at high load for a few hours and then check it

Lydia could be right. If you've got a big alternator that's trying to put 100A into the batteries, it could be too much load on a 20hp engine at idle.

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Capt_Newmo said..
The owner tells me this morning that the 90lt fuel tank has half an inch of sludge in the bottom due to lack of use. Some was sucked up and burnt off so that's what ended up on the water as soot, they ran if yesterday and the water ran clear but still with some soot. He is draining the tank, replacing all the filters and getting a mechanic to look it over.
Lets see what happens.

bullshirt

Just like the old 1/2 tonners for offshore racing, big alternators and single pot motors, so you had a switch, you could motor or you could charge but not both if the batteries were down.
Pics looks just like that.

I thought if this last night on Yanmars not all but in the small earth moving machinery with 30 hp and less
some of the injector pumps can get a problem if some one trys to take a injector pipe off the injector pump even if you just bleeding the injector lines
On some Yanmars ( would be early designs) the fuel adjustment is controlled by this nut under the injector line at the pump


So if you look at these photos you can see a bolt clamp going through just above the top of the pump housing through the lower section of the injector pipe fitting some time if you not careful on some injector pumps they can turn and what that does in enrich the fuel going to that injector.
I've see this while working on old models at least ten years ago but I do not know if the Marine versions use the same injector pump . but make sure you hold the lower section when unding the injector pipe as turning might enrich the fuel

The big question is when was it last started?
If it was run up every fortnight I doubt it would look like this
If the seller was really into selling he would have started it warmed it up before you arrived!
I would BARGIN hard for a cheap price.

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HG02 said..
I thought if this last night on Yanmars not all but in the small earth moving machinery with 30 hp and less
some of the injector pumps can get a problem if some one trys to take a injector pipe off the injector pump even if you just bleeding the injector lines
On some Yanmars ( would be early designs) the fuel adjustment is controlled by this nut under the injector line at the pump


So if you look at these photos you can see a bolt clamp going through just above the top of the pump housing through the lower section of the injector pipe fitting some time if you not careful on some injector pumps they can turn and what that does in enrich the fuel going to that injector.
I've see this while working on old models at least ten years ago but I do not know if the Marine versions use the same injector pump . but make sure you hold the lower section when unding the injector pipe as turning might enrich the fuel

what I mean to say is if you try and bleed am injector line via the bottom pipe nut there is a chance you could turn the nut under it which it how you adjust the fuel amount on that injector

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QLDCruiser said..
Lydia could be right. If you've got a big alternator that's trying to put 100A into the batteries, it could be too much load on a 20hp engine at idle.

100 amps, 14 volts = less than 2 horse power. Not enough to make a 20 HP motor blow smoke. Look at the first photo, that's not smoke, that's a bush fire.

Probably a combination of problems caused by not enough use. I'm surprised the owner did not do a test run before the buyer arrived. I like the idea of the engine struggling to charge a full bank of batteries. I would also consider a blocked exhaust where the salt water enters the exhaust downpipe. This can get restricted when the engine is run for long periods at low revs and no load. Engine will start easy enough and make the right noises but when put in gear will have no power and blow heaps of smoke. The prop would most likely be covered in crap and when you did the test run also cause the engine to blow smoke. So just a heap of small problems that most inactive boats get.

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HG02 said..

HG02 said..
I thought if this last night on Yanmars not all but in the small earth moving machinery with 30 hp and less
some of the injector pumps can get a problem if some one trys to take a injector pipe off the injector pump even if you just bleeding the injector lines
On some Yanmars ( would be early designs) the fuel adjustment is controlled by this nut under the injector line at the pump


So if you look at these photos you can see a bolt clamp going through just above the top of the pump housing through the lower section of the injector pipe fitting some time if you not careful on some injector pumps they can turn and what that does in enrich the fuel going to that injector.
I've see this while working on old models at least ten years ago but I do not know if the Marine versions use the same injector pump . but make sure you hold the lower section when unding the injector pipe as turning might enrich the fuel

what I mean to say is if you try and bleed am injector line via the bottom pipe nut there is a chance you could turn the nut under it which it how you adjust the fuel amount on that injector

i dont think you adjust the fuel amount by adjusting the elements up and down this is done under the plate with the screws in it.the elements are torqued down to a spec some old ones were shimmed to get delivery balance, some, some are adjusted on a rail postilion if it is loose you will get fuel by pass .on old pumps you would remove the delivery valve to set fuel timing as pumps were not mark from the fuel room.if you do this to many times the seal washer would squash and affect the fuel balance and syncro of the pump and individual piston timing, the clamps were there on early pumps to stop elements from vibrating loose. if one comes loose you normally develop a miss and a fuel leak. a incorrectly fitted fuel line would often loosen the elements .

but the engine is providing thrust as well.

that black crap is better out than in ! you should pay more for the yacht now !