Yanmar 2GM20f

[rvennis]

1991 with about 1000 hours; in a C&C 34; mixing elbow, fuel pump, impeller recently replaced; fuel tank removed and completely cleaned; fuel filters replaced regularly; air filter cleaned; starts and runs well.

Recently, I have noticed more black soot appearing on the bottom 10 inches or so of the transom. I cleaned it off yesterday before motoring for about 5 hours at 2800 rpms after which it appeared again.

Can anyone tell me what this may indicate?

[fareweather]

Maybe dirty injectors? Can't hurt to run a bottle of Lubrimoly Diesel purge through it.

Easy Lubro Moly Diesel Purge How-To - with pics!! - TDIClub Forums

[Chief Engineer]

Dirty Bottom

then look at the injectors

[svquest2]

Incomplete combustion. Check Air Filter again, Injectors and timing.

Joe S

[Badsanta]

check your bottom and prop first before you start taking things off.

[GordMay]

Black smoke is generally caused by incomplete combustion, usually due to either overload, or compression or air/fuel mixture problems.

The first & simplest thing to check for is an air inlet restriction such as from a plugged/dirtry air cleaner/filtre. Take off the air filter and make sure the intake port is clear. If the engine still smokes with the port clear and the filter off, the problem is elsewhere.

See also a very old discussion “The Smoking Gun “
Interpreting Diesel Exhaust Smoke:

Goto ➥ http://www.cruisersforum.com/forums/...-gun-1707.html

cruisersforum.com/forums/f54/the-smoking-gun-1707.html