Yanmar 2GM Fuel adjustment

[Sinbad_2]

I've got a problem of lots of black smoke on anything much above 3/4 throttle. (yanmar 2GM in a Jeanneau 30 - 20 years old). A mechanic friend of mine looked at the problem and said that it was mainly unburnt diesel coming out the back. He suggested a number of things, like checking prop size (which is ok), replacing air filter (now done), decoking exhaust manifold (now done). Once all of these things were done he said that I could try reducing the amount of fuel going in if the problem persisted. Unforetunately he's 'moved on' now. There is some sort of adjusting nut on the engine block that looks as if it might adjust something in the fuel injuector pump. I have removed the outer cover nut and there is a adjusting screw inside. At the moment this screwed in all the way. Is this the fuel adjustment? If it is which way does it need adjusting to reduce fuel? (Mucking about with motorbike carbs 20 years ago screwing something in would reduce the mixture - is this the same?) If that is the case the thing is scewed in all the way anyway!

Any thoughts or suggestions would be very welcome. Sorry for long post.

 

[snowleopard]

Had a look in the workshop manual . It says the injection volumes on each cylinder is adjusted separately and they must be the same to within 3% or one cyl will overheat. It looks to be very much a job for a well-equipped workshop /forums/images/graemlins/frown.gif

 

[Bilgediver]

Black smoke on a diesel is a symptom of overload and tweeking isnt the answer as it is the overload which has to be dealt with.

The overload could be due to imbalance of the cylinders..ie one cylinder not giving the power it should..This could be due to valve problems or injector problems..If valve problems then turning the engine over by hand and decompressing the cylinders on at a time might show that one cylinder has much more compression pressure than the other..

To check the injectors then take them to a diesel injection shop.

The above problems would affect starting and the engine would sound like it might be starting on one cylinder with the other cutting in later.
If both cylinders are reasonably balanced then this overload can come from a fouled propeller and or hull...surprising what some weed will do..!!!!!

John

 

[Sinbad_2]

Should have said that hull is clean and injectors have been checked. I've also checked valve clearances and they all ok. According to all sorts of experts at the boat show the prop I have is the right one for the boat, engine and gearbox (Jeanneua 30', 2GM, 2.21:1 and the prop is a fixed 3 blade 14x9)

I haven't checked compression so could do that, but the engine starts and runs well in all ways other than the unburnt diesel at 3/4 plus throttle...

 

[cindersailor]

Sounds very much like an over-sized prop to me, assuming that the air supply to the engine is adequate (try running without the air filter and with the engine compartment open).

Also try running in gear while moored to a pontoon. If the smoke starts at lower revs than while under-way its likely to be the prop. While you are under-way the forward motion of the boat allows the prop to turn more easily, but when moored up this effect is absent. The engine produces max hp at max revs, but if the prop is too big it cannot reach max revs, and by increasing the throttle setting further you are adding more diesel which cannot be burnt at the lower revs - more diesel per compression stroke, but the same amount of air gives unburnt diesel = black smoke. Idealy you should be able to get to max revs (or very close) before black smoke - then you know that the prop is correctly sized.

I went through all this in reverse last year. My prop was too small so I relaced it with a slightly bigger one. Now I get black smoke under-way at about 3200 rpm which is close to max revs (3400) which I am happy with, although weed on the hull reduces this a little. However, when moored up I get smoke at about 2900.