Exhaust smoke and unburnt fuel

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daveperce

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Here's a tale...my yacht has just been given the kiss of life after a 16 month lay-up. I changed all the fuel/oil/air filters and re-filled with new oil. The fuel remaining in the tank (1/2 full) was in good condition and no water in the trap, so I filled the tank. Immediately on launching, the 18hp Yanmar 2GM20 refused to rev beyond 1200rpm and if I pushed harder on the morse, black smoke and unburnt fuel was coming from the exhaust. . As the engine warmed up I was able to coax it to 1700rpm. Interestingly enough at 1100rpm the boat was doing 4.5knts. She is fitted with a 2 blade feathering MaxProp and the boatyard (no names yet, possible legal action) replaced the cutlass bearing - prop removed and refitted. If the prop gearing/pitch was incorrectly set could this explain the smoke et al?? /forums/images/graemlins/confused.gif
 
How long did you run it for?


I wouldn't expect a prop problem to make your engine smoke and spray unburnt fuel out, the two are unrelated!

However, you could have a stuck or dirty injector.

This may disappear after a few hours running, but keep an eye on temperature etc.
 
I disagree. The symptoms are of an overloaded engine. I don't know the ins and outs of a maxprop, but if it's running too coarse that would result in similar symptoms. Could also be the Cutless is to toight on the shaft?
 
From your description of the problem it appears to be that the engine is struggling to drive the prop.

This could be for a number of reasons ~ I assume that the boats bottom is clean as is the prop.

I would put the engine in neutral (and definitely not running) and try to turn the prop shaft by hand ~ it should be relatively easy to turn. If it isn't then you need to check the shaft alignment.
A more complicated check would be to split the shaft from the gear box and run the engine to see if it will rev to 4K.

Peter.
 
You seem to suspect the prop rather than the engine.

Most engines will show smoke but only at full revs under load.
Defective injectors will smoke but the engine should achieve full revs - yours is not making full revs. Will it make full revs without load? Is the running consistent or variable? If the answer is negative to these questions, it could confirm the engine/fuel system as your problem.

I suggest you start your diagnostic with the fuel system. Although you reckon the fuel is ok, try shutting off the fuel supply and inspecting the first fuel filter. If it's crudding up you have the probable cause of under perfomance. It means emptying the tank, cleaning and starting again. Ouch.

That you have been able to coax more revs out of a warmer engine indicates the prop is not so likely to be the cause of resistance - a wrongly reinstalled prop would not respond this way. I would doubt the cutless bearing renewal is your problem; I presume you turned the prop by hand before launch and found the shaft turning freely in the new bearing?

I would check out the engine before entertaining the cost of lifting.

PWG
 
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I disagree. The symptoms are of an overloaded engine. I don't know the ins and outs of a maxprop, but if it's running too coarse that would result in similar symptoms. Could also be the Cutless is to toight on the shaft?

[/ QUOTE ]


He didn't actually specify if it was in, or out of gear at the time.

Therefore I assumed it was in Neutral, as it would be fairly obvious it wasn't a running problem as such if it only did it in gear.... /forums/images/graemlins/confused.gif
 
If the prop was the ONLY problem I doubt that the engine being warm would make a difference but maybe if the cutless was tight it might but but if it were that tight and acting as a brake would the engine be able to drive at gear engagement speed?
to get black smoke from the fuel system does indicate that more fuel is getting to the engine than it is useing perhaps one cyl may not be working .
Try losening each injector pipe slightly in turn and see what effect this has it should be same with both cylinders
A tank left 1/2 full for this length of time is likely to have water in it
Do you know what speed the boat was doing before at the same revs?
 
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I disagree. The symptoms are of an overloaded engine. I don't know the ins and outs of a maxprop, but if it's running too coarse that would result in similar symptoms. Could also be the Cutless is to toight on the shaft?

[/ QUOTE ]


He didn't actually specify if it was in, or out of gear at the time.

Therefore I assumed it was in Neutral, as it would be fairly obvious it wasn't a running problem as such if it only did it in gear.... /forums/images/graemlins/confused.gif

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Interestingly enough at 1100rpm the boat was doing 4.5knts.


Problem with the prop over pitched
 
As I recall, at just over tick-over in gear she would pull about 2.5 knts. The bottom was freshly anti-fouled immediately before she went in. The engine will freely rev in neutral and reverse....just in ahead I have the problem - infact now as soon as I put the engine in forward gear, she stalls!!
 
Gearbox, shaft, sterngland, cutlass, crap round prop.... I would use the reverse order to check. Have you tried it astern?...Ooops yes you have, then looks like a gearbox problem or something binding in ahead that doesn't in astern. does the shaft turn easily by hand witht he engine off and in neutral
 
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I disagree. The symptoms are of an overloaded engine. I don't know the ins and outs of a maxprop, but if it's running too coarse that would result in similar symptoms. Could also be the Cutless is to toight on the shaft?


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The MAxprop is a feathering and not a folding propeller and the pitch at which it deploys to can be adjusted. It seems yours is adjusted for too coarse a setting.

Why not contact MAxProp or get the manual from the web so you can reset it to a lower pitch setting.

You have a lower reverse setting so this is why no problems in astern and expect the astern speed is much less.
 
The shaft turns fine by hand in neutral...I guess I'm going to have to resign myself to a exploratory bill from another engineer!
 
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The shaft turns fine by hand in neutral...I guess I'm going to have to resign myself to a exploratory bill from another engineer!

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As someone mentioned above, it's probably the Maxprop adjustment. The symptoms are just like too big or too coarse a prop
 
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Sounds like too much pitch, therefore engine overloaded causing black smoke and unburnt fuel.

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From various readings here and on the moody Owners forum, I thought unburnt fuel produced white smoke.... cant remember what black smoke was.

i may be wrong!
 
Just go to the Maxprop web page and learn how to reset the prop and make sure your expensive engineer understands these things and doesn t fob you of with wishy washy words and a big bill !!!!!!!!!
 
What is a stuck injector.

I have noticed of late that my port engine (1gm10) is getting quite hard to start. I have done no investigation at all as yet. Lots of smoke and up to 20 seconds with lots of throttle to start. Up until the last few starts it has started with no throttle, pretty much on the button. The engines are 2002 vintage.

Once running it is perfectly fine and has never let me down. I have a full service kit ready, but I don't think it is a service, something has changed.

I was thinking of getting the injector serviced over winter, but your description has me piqued. Stuck sounds like I should try tapping it with a screw driver handle.

What sticks, is it serviceable by me?
 
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