Yanmar 2GM20F . . . Black Smoke

[reiner]

Hi all
We bought our boat about 16 month ago and it has a 2GM20F fitted.
Last week for the first time I tried to full throttle the motor to see what it does.
We get a big cloud of black smoke behind us and can smell the sud . It leaves a black cloud on the water too with is not oil, it looks like carbon.
When I back the throttle off to about 2300rpm all is back to normal.
I wonder if the motor hasn't been run at full throttle for a long time and is just burning off crap or could it be something more than that?
Cheers
Reiner

[DeepFrz]

What RPM do you reach when at full throttle? Maybe you are over propped. Prop could be fouled.

[Chief Engineer]

Bottom or prop fouled

or

you are trying to get it to move past theoretical hull speed

or

excessive back pressure due to clogged elbow

or

dirty injectors

in that order

[reiner]

I think it was just over 3200 rpm, it felt it didn't want to go any higher. The air filter is new by the way , I was thinking maybe not enough air but I don't think that is it.
The prop would have been on the boat since day one (I think).
Which doesn't mean it is the right one.....

[reiner]

Originally Posted by Chief Engineer

Bottom or prop fouled

or

you are trying to get it to move past theoretical hull speed

or

excessive back pressure due to clogged elbow

or

dirty injectors

in that order

The boat has just been on the dry and the prop is clean as a whistle. We got to about 6 knots, hull speed is 7.5
The injectors are 3 years old but the clogged elbow might be an option.
Very hard to get to and I never had it out.
I will look at that.
Thanks for your thoughts