Dearest engine wonks,

I have a yanmar 2gm20f with sd20. When it's cold and it comes under
load (eg. the alternator starts developing more than 20 amps) it is
unable to hold its rpms. Typically it runs easily up to speed but then
as the load kicks in it drops back down to idle and then revs back up
past the throttle setting and then drops back down again. Sometimes is
stalls. Once it has gotten warm it runs like a top. There is no
visible smoke. I have:

replaced the fuel and both fuel filters,
replaced all the washers on the fuel lines and checked for leaks,
taken the injectors to a shop to be checked.

Now, I don't know what to look at next. Any ideas out there?

Thanks,

-- Tom.

Thanks Larry. I've looked really hard for air leaks and fuel leaks...
The fuel tank is higher than the engine and I have bled the thing very
well. I'll look some more, but don't understand why it would get
better when it gets warm... Also, if the engine has been wamed up
sometimes it doesn't have the problem the next day... If it was the
injection pump would it ever run well?

-- Tom.

Could also be water in the fuel.
Check the sump portion of the fuel filters for evidence of free water
..... then be sure to wet the filter cartridge O-rings/seals with fuel
when you reseal them - a possible source of bubbles in Larry's posting.

Flat seals on filter cartridge housings are notorious 'leakers' and
must be installed 'wetted' with fuel oil so that you insure that they
seal.


In article .com,
" wrote:

Thanks Larry. I've looked really hard for air leaks and fuel leaks...
The fuel tank is higher than the engine and I have bled the thing very
well. I'll look some more, but don't understand why it would get
better when it gets warm... Also, if the engine has been wamed up
sometimes it doesn't have the problem the next day... If it was the
injection pump would it ever run well?

-- Tom.

" wrote in
oups.com:

Thanks Larry. I've looked really hard for air leaks and fuel leaks...
The fuel tank is higher than the engine and I have bled the thing very
well. I'll look some more, but don't understand why it would get
better when it gets warm... Also, if the engine has been wamed up
sometimes it doesn't have the problem the next day... If it was the
injection pump would it ever run well?

-- Tom.



As things heat up they get bigger, sealing the hole, probably. If your
fuel tank is higher, gravity pressure should make it so there's no vacuum
in the whole system...so there should be no bubbles, only diesel fuel
leaking into the hull. Hmm....might be more of injection pump problems.

Has anyone done a compression test on it? How many hours are on it??

Rich Hampel wrote in news:290320062253232580%RhmpL33
@nospam.net:

Flat seals on filter cartridge housings are notorious 'leakers' and
must be installed 'wetted' with fuel oil so that you insure that they
seal.


I'd have been with this all the way, but he's not pulling a vacuum on the
tank as the tank is higher than the engine. If the gasket were leaking,
his bilge would have fuel in it.

I'd like to see that water test, too. Way too many boaters are too eager
to get back to the dock with guests and leave the poor thing sitting there
with half-empty tanks to breathe the water in every night. They don't want
to be bothered buying 8 gallons of fuel, so the tanks get to breathe and
the problem starts. It's so easy to prevent water in the tanks. It's not
in the fuel you buy at all.

Regarding air leaks:

I had a impossible to find air leak, which I could not detectable. Over a
period of a year I went over every aspect of the engine with out success. I
finally took apart the fuel line going into and exiting the fuel filters
(frams). I took apart the couplings for the water and fuel filter units. I
reinstalled everything using Teflon tape on all threads. My problem went
away.

stu



wrote in message
oups.com...
Dearest engine wonks,

I have a yanmar 2gm20f with sd20. When it's cold and it comes under
load (eg. the alternator starts developing more than 20 amps) it is
unable to hold its rpms. Typically it runs easily up to speed but then
as the load kicks in it drops back down to idle and then revs back up
past the throttle setting and then drops back down again. Sometimes is
stalls. Once it has gotten warm it runs like a top. There is no
visible smoke. I have:

replaced the fuel and both fuel filters,
replaced all the washers on the fuel lines and checked for leaks,
taken the injectors to a shop to be checked.

Now, I don't know what to look at next. Any ideas out there?

Thanks,

-- Tom.

On Thu, 30 Mar 2006 08:54:32 -0600, "West Indies"
wrote:

I took apart the couplings for the water and fuel filter units. I
reinstalled everything using Teflon tape on all threads. My problem went
away.

Unfortunately teflon tape has a reputation for degrading over time
when in contact with diesel fuel. Professional mechanics use a
special blue paste to seal fuel fittings.

I took apart the couplings for the water and fuel filter units. I
reinstalled everything using Teflon tape on all threads. My problem went
away.


There can be air leaks in other places than threaded joints.


Wayne.B wrote:
Unfortunately teflon tape has a reputation for degrading over time
when in contact with diesel fuel. Professional mechanics use a
special blue paste to seal fuel fittings.


IIRC there is tape rated for use with various petrochemicals
& solvents... a bigger problem is that little shreds of tape
get in the injection system. Not good.

Fresh Breezes- Doug King

I haven't done a compression test on it. It puts out full power as far
as I can see -- its a catamaran and the identical engine on the other
w/identical prop doesn't do any better power wise at WOT. Have this
vague idea that it might be a tiny leak in the water jacket but there
is no obvious steam and it doesn't blow water out of the reservoir. It
has about 1200 hours. We cruise in the South Pacific full time so we
take awful fuel and often run the tanks pretty low on passages.
However, the fuel that is in there now is New Zealand fuel and I took
it all out and ran it through a double filter set-up so I'm thinking
its pretty dry...

In my search for leaks I have pulled the engine out and painted it and
cleaned the bilge to surgical standards. I'm pretty sure that no
significant fuel leaks into the boat... If we're leaking into the
crank oil it isn't raising the level noticeablely...

Many thanks to all for the thoughts -- I'm looking at each carefully
and even running the engine as I type.

-- Tom.

" wrote in
oups.com:

If we're leaking into the
crank oil it isn't raising the level noticeablely...



The old 4-108 Lionheart came with had like 9000 hours on it and little
maintenance. There was a good bit of unburned diesel oil leaking past
the worn-out rings, but it just ran and ran. The current engine was a
pullout from a nice fellow (who may be watching this...(c in Oriental,
NC. I met him on this newsgroup and my captain/owner bought the
engine/transmission from him for $1200, I think. Lionheart's original
transmission is the hydraulic one that can freewheel forever because
Lionheart has a shaft alternator producing 15-20A of charging current at
8-10 knots off her fixed screw. The more recent transmission was not, so
the engine ship switched them. The old engine is in Marietta, GA, in the
captain's garage, last I knew. He was going to rebuild it, but hasn't.

They're great engines. Ours flooded 3 of 4 cylinders with seawater
between Ft Lauderdale and Ponce Inlet to Daytona when it was locked up,
solid. Towed the long way to Daytona Marina up the ditch, Cutter Doc was
hired to fix it and he came that night to pump the Exxon Valdez oil slick
out of the Perkins' bilge. It had tar balls in it! One injector mount
was cracked and 2 injectors were trashed. We changed the oil a "few
times" until pumping it out looked something like oil, then reinstalled
the injectors and she cranked right up. It's been running flawlessly
ever since. The new engine had nicer controls and working guages, too.
We can even read oil pressure and water temperature, now...(c;

Reliable old tractor engine....English like my captain!