120 Lehman Stalls at Full Throttle

[Hutch9900]

Hi everyone! My name is John and I just purchased a 1982 Marine Trader 34 DC. We are super happy with the boat so far and cannot wait to absorb some of the knowledge in this community. We have owned two other boats, both I/O (one a cuddy and the other PC). I have never owned a diesel before.

So, we took the boat out this past weekend and enjoyed a wonderful cruise of about 20 NM. I did slowly increase the throttle to full and after a minute the engine died. It would fire right back up and all temp and oil pressure was fine. As long as I stayed at 1800 rpm or below it would not stall. Has anyone ever heard of this problem? What is the typical performance should I expect (max rpm, best economical cruise, etc.)? Thank you all in advance for any information!

 

[RT Firefly]

Greetings,
Welcome aboard. Check your fuel system (filters, collapsing fuel lines etc). Sounds like fuel starvation to me. I'm assuming Lehman 120HP. Typical "performance" is about 2500 RPM wide open throttle and I've found just below hull speed (about 7 knots) to be MY most economical cruising speed. With our 34' that was about 1750 RPM.
Enjoy...

 

[Hutch9900]

Thank you so much! I will definitely check the fuel lines. They are mostly copper if I am not mistaken and the fuel filters are all brand new, as it was serviced right before I purchased. At 1700-1800 rpm I was doing 7.5knts so sounds about what I am getting. I forgot to look at the WOT rpm but think it was around 2100-2200.

 

[Hutch9900]

And yes, sorry I should have mentioned FL120.

 

[BruceK]

As well as filters(were they correctly fitted?),check the vent to the fuel tank is not partly blocked

 

[rgano]

Mr FF is telling you for true, but aside from that, anything over 1800 RPM is too fast to run the FL120, especially in a 32-foot boat.

 

[Hutch9900]

Rgano, thank you for letting me know that! I wasn't sure if I needed to run her WOT from time to time to make sure it burns clean. I have read that in some places about diesels and wasn't sure how it applies to a boat. Mine is a 34 and dry weighs about 20k lbs.

 

[RT Firefly]

Greetings,
Mr. H. No need to run WOT to "clean" a Lehman, IMO. On rare occasions (maybe once or twice a year) I do run up to WOT for a very short time (less than 30 seconds) just to see if WOT is still achievable. American Diesel is a GREAT source for parts AND information. https://americandieselcorp.com/

 

[Hutch9900]

RT,

Well that is a great resource for sure! I'm so glad you mentioned them already. Love that they have kits on the ready for newbies like myself

 

[Comodave]

Sounds like a fuel starvation issue. Check the filter elements and see if they are dirty. Usually they will be Racor filters.

 

[kchace]

Hi everyone! My name is John and I just purchased a 1982 Marine Trader 34 DC. We are super happy with the boat so far and cannot wait to absorb some of the knowledge in this community. We have owned two other boats, both I/O (one a cuddy and the other PC). I have never owned a diesel before.

So, we took the boat out this past weekend and enjoyed a wonderful cruise of about 20 NM. I did slowly increase the throttle to full and after a minute the engine died. It would fire right back up and all temp and oil pressure was fine. As long as I stayed at 1800 rpm or below it would not stall. Has anyone ever heard of this problem? What is the typical performance should I expect (max rpm, best economical cruise, etc.)? Thank you all in advance for any information!

Your problem is most likely fuel starvation. When it happens with the symptoms you’re experiencing it’s usually a clogged primary filter (the off engine Racor)I would change that first.

Ken

 

[jleonard]

The short flexible rubber line that enters the fuel lift pump is notorious for delaminating inside and collapsing.
You could also have plugged/partially blocked fuel tank vents.
I used to run my Lehman up to WOT several times each season to make sure everything was working well. Always did it on my last leg before I entered my home harbor.

 

[Hutch9900]

Thanks guys! I will check the filter, vent and fuel line. Curious if I have to purge the fuel lines and if changing the filter will make it really hard to get the engine started again? I have heard these can be hard to start after changing the filters. Any tips would be greatly appreciated.

 

[RT Firefly]

Greetings,
Mr. H. Yup. Sometimes it IS necessary to bleed your fuel system after changing filters. Depends on the circumstances/engine(s)/filter mount configurations. There are probably several threads on the subject but, MY memory is SO bad I am unable to point you in that direction. Do a search for "bleeding fuel lines" and you'll probably find some tips or procedures.


Once you figure out what you have to do for YOUR set-up, it's actually quite easy. Any air in the fuel delivery system can cause problems.

 

[SteveK]

The fuel tank vent line is often mentioned as being plugged. OK, say it is. Can someone explain how to get it unplugged?

Hutch, meanwhile you can remove the fuel fill cap just before doing wot and if the same problem occurs then it is not the fuel tank vent.

 

[Gdavid]

The fuel tank vent line is often mentioned as being plugged. OK, say it is. Can someone explain how to get it unplugged?

Many vent fittings on the hull have a little screen on it to prevent stuff from getting in (bugs I guess), they get corroded and restrict air flow, not totally air tight but enough of a restriction to make fueling miserable. Otherwise the vent line could get kinked or delaminate internally but the screens are the most common problems in my experience.

 

[Hutch9900]

Thank you Gdavid and Soo! Both helpful starting points to check and easy enough for a novice like me.

 

[Marco Flamingo]

Doesn't sound like a slow fuel starvation to me. It gets fuel at lower rpms. The engine stalled and dies above 1,800. If starvation, I would think that the engine would run rough, lose rpms, then be back in the range where the hoses, filters, whatever, would pass sufficient diesel to try to get back up above 1,800 again. It would be a rough, searching situation. Not a phht, dead situation.

That being said, I don't have an answer.

 

[jleonard]

Doesn't sound like a slow fuel starvation to me. It gets fuel at lower rpms. The engine stalled and dies above 1,800. If starvation, I would think that the engine would run rough, lose rpms, then be back in the range where the hoses, filters, whatever, would pass sufficient diesel to try to get back up above 1,800 again. It would be a rough, searching situation. Not a phht, dead situation.

That being said, I don't have an answer.

The delaminated hose I described above happened to me. The engine just would die. A new hose and lift pump solved it. The pair came in a kit from ADC

 

[bligh]

The delaminated hose I described above happened to me. The engine just would die. A new hose and lift pump solved it. The pair came in a kit from ADC

So was it the hose or the lift pump?

 

[Choices]

You need to find a dock buddy with a well tended Lehman. He can teach you alot. Vacuum gauges will also help.

 

[jleonard]

So was it the hose or the lift pump?

I'm convinced it was the hose based on ADC's information. But since the original pump had 3000+ hours on it, and the new fittings/hose was different, I decided to change both.
After I had it running again, I changed the filtration arrangement to multi-stage.
And for the following 14 years and almost 2000 hours, never another fuel problem.

 

[BeeJay]

A long shot - does it have an air filter fitted.

 

[kchace]

Thanks guys! I will check the filter, vent and fuel line. Curious if I have to purge the fuel lines and if changing the filter will make it really hard to get the engine started again? I have heard these can be hard to start after changing the filters. Any tips would be greatly appreciated.

Generally Lehman’s do not need to be bled after changing the primary filter. Open the top, pull out old filter, install new filter, top up with diesel, put top back on. Done.

Ken

 

[Comodave]

The secondaries are the PITA to bleed on a Lehman. Be very careful that you get all the old gaskets and O rings out before reassembling the filter. Also be aware that all of the seals are not O rings some are square gaskets and if they get a twist then they will leak.

 

[rgano]

Bleeding the FL120

I believe I had the best filter priming and bleeding system on my trawler for my twin 120s and Onan genny. A couple of photos will help. Firstly, you may already be acquainted with the awkward and sometimes painful manual flipper on the lift pump on the right side of the engine. Best if you can avoid using that thing. Next, you may be aware of the vents on the secondary fuel filters on the engine. Best to avoid them too.

The smartest thing I ever did with my fuel system was to take the advice of the Ford Lehman dealer in San Diego to let them install a Facet Fuel pump into the system with a bypass valve and hose around it. It is shown in the photo circled in blue. The red-handled bypass valve is in the normal bypass position allowing fuel to flow through both the pump and around it. Shut that and energize the pump to pressurize the fuel system.

Whenever bleeding was needed or when I had a pesky air ingestion issue in an engine, I simply switched on this pump (leaving it on if it was air ingestion) and bled the whole fuel supply system at the injector pump (see next paragraph).

The other photo shows were to bleed a Simms type injector pump. That is a 1/2 inch bolt you just crack open and place a rag there to soak up fuel until it flows with no air bubbles. Sorry for the dirt and grit here - I had just fished a lot of overhead work. If you bleed from here, there is no more air anywhere in the system, and the engine will instantly start.

 

[jleonard]

Here is another system using an electric fuel pump for priming.

 

[slowgoesit]

Lots of good advice here, please let us know what you figure out to be the problem as it will help others if they search the forum with a similar problem!
Also, Welcome to the Forum! It's a nice place to hang out, but watch out, if you're not careful, you'll LEARN SOMETHING!

 

[rgano]

Here is another system using an electric fuel pump for priming.

A Walbro. Good pump. I had one in the polishing system I installed in my trawler.

 

[Marco Flamingo]

One of the nice things my PO did was a polishing system that can also bleed the fuel line. The various 3-way valves were labeled #1, #2, #3, etc. I didn't get the code book with the boat and it took some head scratching to figure out.