I have a reasonably well used 2GM. Its top speed should be 3600 rpm,
and it has always been able to reach that speed under load. I
normally cruise at 2700, by the way.

This year, the engine will go to 3600 in neutral, but only to 2800
under load.

What I've eliminated -

Its not a control problem, the fuel control on the engine is against
its stop when full on.

I've replaced the fuel lift pump, with no change.

I've replaced all the fuel filters, with no change.

I've run the engine without its air filter, with no change.

Its not a tach problem - in neutral the engine runs at 3600.

There is no smoke at full throttle under load, which makes me think
this is NOT an injector/pre-combustion chamber problem.

I'm not burning oil, although I haven't checked compression. The
engine starts without trouble.

I'm trying to list the possible causes, and ways to do diagnosis.

My list -

A governor problem. If so, I don't know what to look at first, or how
to test.

A high pressure fuel pump problem.

Air leak in the fuel system. (Would that cause this, but no other problems?)

Exhaust back pressure.
--

x-no-archive:yes
Marc Auslander wrote:

Are you sure the prop is free of growth?

I have a reasonably well used 2GM. Its top speed should be 3600 rpm,
and it has always been able to reach that speed under load. I
normally cruise at 2700, by the way.

This year, the engine will go to 3600 in neutral, but only to 2800
under load.

What I've eliminated -

Its not a control problem, the fuel control on the engine is against
its stop when full on.

I've replaced the fuel lift pump, with no change.

I've replaced all the fuel filters, with no change.

I've run the engine without its air filter, with no change.

Its not a tach problem - in neutral the engine runs at 3600.

There is no smoke at full throttle under load, which makes me think
this is NOT an injector/pre-combustion chamber problem.

I'm not burning oil, although I haven't checked compression. The
engine starts without trouble.

I'm trying to list the possible causes, and ways to do diagnosis.

My list -

A governor problem. If so, I don't know what to look at first, or how
to test.

A high pressure fuel pump problem.

Air leak in the fuel system. (Would that cause this, but no other problems?)

Exhaust back pressure.

grandma Rosalie

i've only been to 2 of my diesel-for-yachts classes, but the fast answer
from those classes was - if it can hit max rpm in neural but not under
load, it is something about the boat or prop. not a new prop, i assume ...

I'm pretty sure the prop is NOT the problem. I've looked at it in the
water, and its clean. And its the same prop that got to full speed
last year. Should have put that on my initial list - sorry and thanks
for the reminder.
--

Sounds like your prop is fouled with barnacles since it previously
ran OK. Otherwise I would guess that it is overproped.

Doug

"Marc Auslander" wrote in message
...
I have a reasonably well used 2GM. Its top speed should be 3600 rpm,
and it has always been able to reach that speed under load. I
normally cruise at 2700, by the way.

This year, the engine will go to 3600 in neutral, but only to 2800
under load.

What I've eliminated -

Its not a control problem, the fuel control on the engine is against
its stop when full on.

I've replaced the fuel lift pump, with no change.

I've replaced all the fuel filters, with no change.

I've run the engine without its air filter, with no change.

Its not a tach problem - in neutral the engine runs at 3600.

There is no smoke at full throttle under load, which makes me think
this is NOT an injector/pre-combustion chamber problem.

I'm not burning oil, although I haven't checked compression. The
engine starts without trouble.

I'm trying to list the possible causes, and ways to do diagnosis.

My list -

A governor problem. If so, I don't know what to look at first, or how
to test.

A high pressure fuel pump problem.

Air leak in the fuel system. (Would that cause this, but no other
problems?)

Exhaust back pressure.
--

It could be that the spring that connects the speed control to the governor
has lost some strength.
When the engine reaches full revs the convener closes the fuel supply to the
injector pump to slow the engine. If you want full revs the throttle pulls
the governor lever back using a connection with a spring. spring.
When the engine is not under load you don't have to pull the controls so far
and the spring does not stretch so much to get full revs. Under load the
throttles is pulled all the way down.

Is there more drag than normal on the prop. i.e. stuffing box too tight.
Does the engine get too hot. May be thermostat is rusted partly open but not
open enough?
I have a 3GM

Barry

"Marc Auslander" wrote in message
...
I have a reasonably well used 2GM. Its top speed should be 3600 rpm,
and it has always been able to reach that speed under load. I
normally cruise at 2700, by the way.

This year, the engine will go to 3600 in neutral, but only to 2800
under load.

What I've eliminated -

Its not a control problem, the fuel control on the engine is against
its stop when full on.

I've replaced the fuel lift pump, with no change.

I've replaced all the fuel filters, with no change.

I've run the engine without its air filter, with no change.

Its not a tach problem - in neutral the engine runs at 3600.

There is no smoke at full throttle under load, which makes me think
this is NOT an injector/pre-combustion chamber problem.

I'm not burning oil, although I haven't checked compression. The
engine starts without trouble.

I'm trying to list the possible causes, and ways to do diagnosis.

My list -

A governor problem. If so, I don't know what to look at first, or how
to test.

A high pressure fuel pump problem.

Air leak in the fuel system. (Would that cause this, but no other
problems?)

Exhaust back pressure.
--

Stuffing box too tight ?!!

Marc Auslander wrote:
I'm pretty sure the prop is NOT the problem. I've looked at it in the
water, and its clean. And its the same prop that got to full speed
last year. Should have put that on my initial list - sorry and thanks
for the reminder.

RichH wrote:

Stuffing box too tight ?!!

shouldn't it put out black smoke if it is getting plenty of fuel, but can't
reach rpm because of load?

Marc Auslander wrote in message ...
I'm pretty sure the prop is NOT the problem. I've looked at it in the
water, and its clean. And its the same prop that got to full speed
last year. Should have put that on my initial list - sorry and thanks
for the reminder.
--

Loss of RPM could be an indicating problem caused by oil on the fly
wheel and tach transducer.
With the engine warm and transmission in nutral advance the throuttle
to full RPM 3400. If the engine does not reach the governed setting
the problem is in the indicating system and not the engine.
If the problem is the engine check the exhaust elbo for reduction in
opening. To check elbo remove large hose from elbo and slide two
fingers up inside. If two fingers won't fit through at the top replace
the elbo.

From the author of books on boat refrigeration
http://www.kollmann-marine.com

Marc Auslander wrote:

I'm pretty sure the prop is NOT the problem. I've looked at it in the
water, and its clean. And its the same prop that got to full speed
last year. Should have put that on my initial list - sorry and thanks
for the reminder.


How about the boat speed? Is it the same or nearly? You *are* doing
this with a moving boat? (Ours is limited while at the dock though we
get our 3500 target while moving.)

Other than that, from the list that you first gave, it sure sounds like
when we had a mostly plugged fuel filter..... The engine would wind up
to a certain point and no further. In our case, advancing past that made
the revs drop fairly quickly, killed the engine, and sucked air in, but
you might have a tighter system or less constriction...

--
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/