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Old June 8th 06, 06:17 PM posted to rec.boats.cruising
Drew
 
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Default lehman 120 rough idle

I have a chb trawler with a lehman 120, the motor starts great and runs
well initially, however after a half hour or so, the engine starts
idleing very rough, boat shakes quite a bit, is this an issue with the
injectors, could this be air getting in somewhere, can anyone please
help me out.... how should I diagnois this?


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Old June 8th 06, 07:43 PM posted to rec.boats.cruising
C. S.
 
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Default lehman 120 rough idle

I had exactly the same problem with a small Perkins. The opening pressure in
one injector was way too low. When a second injector reached the same state
the engine refused to start. It has 3 cylinders.
Have your injectors checked, it will probably cure the problem.
When I had that problem it was only while idling and disappeared when I
increased engine speed.

C.S.

"Drew" wrote in message
oups.com...
I have a chb trawler with a lehman 120, the motor starts great and runs
well initially, however after a half hour or so, the engine starts
idleing very rough, boat shakes quite a bit, is this an issue with the
injectors, could this be air getting in somewhere, can anyone please
help me out.... how should I diagnois this?



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Old June 8th 06, 07:52 PM posted to rec.boats.cruising
Larry
 
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Default lehman 120 rough idle

"Drew" wrote in news:1149787059.212252.307340
@i40g2000cwc.googlegroups.com:

could this be air getting in somewhere,


From the tank to the suction side of the primary fuel pump, including
those filters. I agree...air leak making bubbles in the fuel.

It's still leaking at higher throttle settings, but the injectors are
open further under the load so the same size bubble doesn't make as much
difference.

Idle it at the dock. Shut off the fuel valve on the tank. Let it run a
while or until it start to balk. Are the fuel filters still completely
full? Yes? (after the filter) No....the filter itself or before the
filter.

No, you can't fix a leaky hose by overtightening the hose clamps....(c;

Another possibility often overlooked.......

Run it until it starts to run like crap.
Unscrew the filler cap on the fuel tank.
Did you hear it sucking air around the cap, indicating the engine was
pulling a vacuum on the fuel tank because the VENT IS CLOGGED?

Damned Dirt Dauber Wasps, anyways....

Look on the boater's face who'd been looking for the airleak for months
when I found the dirt dauber's nest in the vent pipe?.....PRICELESS...(c;

Just enough air leaked around or through the mud nest to relieve the
vacuum after the motor had been shut down for an hour. Start the motor
back up, she ran like a jewel....well, until the fuel pump lost the
battle with the vacuum in the tank an hour after the next engine start.

Sound familiar??

When it starts to run like crap, crack open the fuel filler cap and see
if that smoothes it back out pretty quick. Vent clogged if it does.

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Old June 9th 06, 02:39 AM posted to rec.boats.cruising
DSK
 
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Default lehman 120 rough idle

"Drew" wrote
could this be air getting in somewhere,



Larry wrote:
From the tank to the suction side of the primary fuel pump, including
those filters. I agree...air leak making bubbles in the fuel.


If it were the injectors, there would be some smoke from the
exhaust when the problem was occuring, wouldn't there?


It's still leaking at higher throttle settings, but the injectors are
open further under the load so the same size bubble doesn't make as much
difference.


Hmm, but it would also be pulling a higher vacuum on the
fuel system, and probably pulling in more air, I would
think. It may run more smoothly but surge somewhat due to
the uneven fuel burn.



Idle it at the dock. Shut off the fuel valve on the tank. Let it run a
while or until it start to balk. Are the fuel filters still completely
full? Yes? (after the filter) No....the filter itself or before the
filter.

No, you can't fix a leaky hose by overtightening the hose clamps....(c;

Another possibility often overlooked.......

Run it until it starts to run like crap.
Unscrew the filler cap on the fuel tank.
Did you hear it sucking air around the cap, indicating the engine was
pulling a vacuum on the fuel tank because the VENT IS CLOGGED?

Damned Dirt Dauber Wasps, anyways....


Wouldn't it be just as easy to check the vent?


Look on the boater's face who'd been looking for the airleak for months
when I found the dirt dauber's nest in the vent pipe?.....PRICELESS...(c;

Just enough air leaked around or through the mud nest to relieve the
vacuum after the motor had been shut down for an hour. Start the motor
back up, she ran like a jewel....well, until the fuel pump lost the
battle with the vacuum in the tank an hour after the next engine start.

Sound familiar??

When it starts to run like crap, crack open the fuel filler cap and see
if that smoothes it back out pretty quick. Vent clogged if it does.


And it's hard on the fuel pump & injector pump.

Since this is a Lehman, you're in luck. Call American Diesel
in Kilmarnock, Virginia. They know more about these engines
than everybody else in the world put together. They're also
friendly & helpful folks.

Fresh Breezes- Doug King

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Old June 9th 06, 04:03 AM posted to rec.boats.cruising
Larry
 
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Default lehman 120 rough idle

DSK wrote in
:

"Drew" wrote
could this be air getting in somewhere,



Larry wrote:
From the tank to the suction side of the primary fuel pump, including
those filters. I agree...air leak making bubbles in the fuel.


If it were the injectors, there would be some smoke from the
exhaust when the problem was occuring, wouldn't there?


Only if it were running RICH. Bubbles and fuel starvation don't smoke at
all. Black smoke - too much load or running rich. White smoke - burning
oil, or if it's steam, dread the thought, head gasket or cracked
head...yecch.



It's still leaking at higher throttle settings, but the injectors are
open further under the load so the same size bubble doesn't make as
much difference.


Hmm, but it would also be pulling a higher vacuum on the
fuel system, and probably pulling in more air, I would
think. It may run more smoothly but surge somewhat due to
the uneven fuel burn.

Not if the vent is open. The suction side of the primary pump only sees
the suction caused by the fuel being lower than the pump. Even wide open
straining away at some god-awful...what?...3200 RPM?...(c;...fuel flow is
measured in hours, thank god at these prices, not gallons per minute
which would make a suction from the hose size like a garden hose.



Idle it at the dock. Shut off the fuel valve on the tank. Let it
run a while or until it start to balk. Are the fuel filters still
completely full? Yes? (after the filter) No....the filter itself or
before the filter.

No, you can't fix a leaky hose by overtightening the hose
clamps....(c;

Another possibility often overlooked.......

Run it until it starts to run like crap.
Unscrew the filler cap on the fuel tank.
Did you hear it sucking air around the cap, indicating the engine was
pulling a vacuum on the fuel tank because the VENT IS CLOGGED?

Damned Dirt Dauber Wasps, anyways....


Wouldn't it be just as easy to check the vent?


Not easy on boats with fuel tanks buried to hide them with vent hoses
behind them to a hull fitting under the toerail. Cracking the fuel
filler to listen for a suction being relieved is the easiest way at the
point when it starts running like crap from fuel starvation.



Look on the boater's face who'd been looking for the airleak for
months when I found the dirt dauber's nest in the vent
pipe?.....PRICELESS...(c;

Just enough air leaked around or through the mud nest to relieve the
vacuum after the motor had been shut down for an hour. Start the
motor back up, she ran like a jewel....well, until the fuel pump lost
the battle with the vacuum in the tank an hour after the next engine
start.

Sound familiar??

When it starts to run like crap, crack open the fuel filler cap and
see if that smoothes it back out pretty quick. Vent clogged if it
does.


And it's hard on the fuel pump & injector pump.

Since this is a Lehman, you're in luck. Call American Diesel
in Kilmarnock, Virginia. They know more about these engines
than everybody else in the world put together. They're also
friendly & helpful folks.

Fresh Breezes- Doug King


Not sure how hard it is on either a diaphram pump or little piston
primary pump. I never saw it hurt anything but pride if it choked to a
stop...(c; Hell you're fuel starving it every time you run it....turning
it OFF!...

You're right on Lehmans, and other British tractor diesels, like our
Perkins. Amazing how rugged a tractor engine really is. The Perkins
with 9000 hours on it we took out cranks right up and runs quite
smoothly....






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