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.

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

In article ,
Wayne.B wrote:

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'm thinking a leak like this, as well. Perhaps simply reseating all the
connections -- don't overtorque -- might find the problem. I'd also look
to the bleeding valves, all three on the 2GM20F. New "wetted" gasket on
the primary filter (on the engine) might solve it.

That type of surging usually points to an air leak, one too small for
diesel.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

I have removed all the fuel lines and the primary filter and replaced
the washers and gaskets and retorqued the lines. If there is a leak
I'm not sure what to test next. I am wondering if maybe the governor's
injection limiter setting is wrong. The manual makes it look easy to
adjust, but I'm guessing that they seal them at the factory for a
reason... Any thoughts on the advisability of fiddling with it or with
the likelihood that it might be the problem?

-- Tom.