Gm30 Brown slick from exhaust

[jpd1]

Originally Posted by GordMay

http://www.cruisersforum.com/forums/...test-1420.html

Thanks for the link, will try that.

[Alan Wheeler]

Do follow Gords post. However, I am not sure this wil tell you anything in this instance. So lets get back to some basics. It is always important to cover things in a few steps at a time and to stick to sound principles, or things get messy real quick. So what we know. by the way, if I have anything wrong here, let me know.
Engine starts OK
Engine revs to max RPM under no load
Engine revs to 3200RPM loaded. By the way, it doesn't make too big a difference tied up or moving.
2500RPM produces black smoke in large quantities.
I am worried about your aircleaner. This seems like it has got a lot of soot blocking it. Although I note you said you ran the engine with it removed and no difference. I do think it worthwhile following the lead of "is something blocking the intake further in" scenario. Black smoke is a major lack of air to fuel ratio. That lack of air to fuel can be over loaded engine or restricted air into the engine. Overloaded can be prop, but not normally hull being dirty. Dirty hull will slow you and cost you fuel, but does not load the engine. Hence having the boat tied to the dock should not be any detrimental affect to the engine load.
I doubt you will see a spray pattern issue by the way. But a spray pattern issue could indeed cause your problem. Especially if you have hgad water in the system. Water will explode in the injector tip and it can chip the tip. Certainly check it if you want. But be very careful. What you do is wrap a rag around the injectors to absorb the fuel spray. Only uncover the one injector at a time. It can come out as a fine mist, which by the way, is actually not what they should do and that mist is dangerous to breath. So the rag is to keep that under control in the engine compartment. The spray pattern should not be a dribble or single squirt either. It needs to be a spray. However, there is one thing you can't test for and that is more important. It is the lift or break pressure of the injector seat. It has to lift at a set pressure. A poor spray pattern can be an issue that can cause this problem. However, you would normaly see it when reving the engine under no load. Lets ope in this case I am wrong. Injectors and air filter are the easy parts to solve.

[jpd1]

Hi Alan

Thanks for the indepth reply

Originally Posted by Alan Wheeler

Engine revs to 3200RPM loaded. By the way, it doesn't make too big a difference tied up or moving.

In this instance it does make a big difference, tied up on the mooring in reverse can be reved to 4000rpm with no smoke or soot. Under nomal motoring load revs will not go above 2800 - 3000rpm with the smoke and large trail of soot deposit from exhaust.

This in some way would point to weed / prop, but have cehcked prop is not fouled, weed growth less than last year (under sail no problem with weed drag)

Its certainly got us scraching our heads and going in circles!

[George P]

Alan, looks like jdp1, if I understand correctly, only loads the engine in reverse at the dock.....maybe it should be loaded in forward at the dock since that's when he gets the smoke and no smoke when loaded in reverse. if this engine can rev to 4000 in neutral then it should rev to at least 3500 when in gear....regardless looks like a prop problem to me, is there any vibration when in forward?

[jpd1]

Originally Posted by George P

Alan, looks like jdp1, if I understand correctly, only loads the engine in reverse at the dock.....maybe it should be loaded in forward at the dock since that's when he gets the smoke and no smoke when loaded in reverse. if this engine can rev to 4000 in neutral then it should rev to at least 3500 when in gear....regardless looks like a prop problem to me, is there any vibration when in forward?

Thanks for the reply

We have tried in forward whilst tied at the marina (although briefly) with no skoke / soot problem.

No vibrations or any reason to suspect prop which haas been previously used with no problems last season.

We can not understand why we cannot creaate problem when trying whilst teathered in the mariana and can build up rpm, but not whilst at sea.(max 2800 - 3000 with smoke & soot)

Air inlet manifold has also been removed today and appears to be clear (no sign of where old filter went?)

Exhaust mixer checked and clear

[Alan Wheeler]

That simply does not make sense. OK, back to a further basic.
Engine should reach max RPM unloaded. Yes it does.
Engine in gear, should now reach within 10% of that RPM. So it should reach 3600RPM in gear. Any less than that and the prop is too big.
It will black smoke if a greater than 10% reduction.
But now you are saying it doesn't tied to the dock, but does underway.
OK, so what is different while underway. How does your engine get air into it's compartment while underway??
Is their any chance that while testing at the dock, you had that compartment open and closed while under way???

[jpd1]

Well I'm glad its not just me that's confused by this!!

Engine compartment was closed with steps to cabin cover and in an identical position to moored up testing.

Most of the testing done whilst in reverse gear due to mooring and will reach full revs.

[jpd1]

Ok - just an update on the ongoing saga.

Problem is now getting worse, now smoking with soot in marina even in neutral at high rev's.

Injectors have been replaced
Mixing elbow checked and clear
Drop test carried out - OK
Air manifold removed and no signs of old air filter
50cm2 vents into engine compartment


Confused when return fuel line disconnect from injectors and put into bottle even at high rev's no excess fuel is passing through, is this right?

Any more advice guys?

Thanks

[never monday]

have either of the circled screws in this picture been adjusted?

[jpd1]

Thanks for the reply

The lower of the 2 screws had sheard off and has been remade and replaced, this seemed to be the engine idle which has been set at 850rpm is that correct? although this only occured after the problem had started whilst trying to find the problem cause.

The upper top screw, what is this one? whilst having problems bleeding the diesel last year, I started to turn and once reliased there was a tag going through it stopped. I have since removed the top which seems to be a cover with a screw and locking nut beneath which has not been adjusted.

Thanks

Look forward to so more info

[never monday]

That's not the idle screw.
It's what can be best described as the mixture screw. If you have a factory manual. There is a procedure for reseting it to the proper position.
4000RPM in gear is too high. The no load limit on that engine is 3850. In gear it should reach 3600-3700.

[jpd1]

Hi Never Monday

Thanks again

What is the top screw adjustment for?

I have been having problems getting a manual in Turkey, will try again to set mixture.

Unfortunatley local Yanmar service agent is not very helpful, so having to muddle through.

[never monday]

the top screw is the max speed adjustment. These are factory set and shouldn't be adjusted. It's to late for that now. Leave the max speed alone and get the fuel right first.

[Alan Wheeler]

great info Pat. Nice to see you around by the way. It's not the same without you around here.