Throttle Linkage Adjustment Question

I have an American Diesel, 139 HP with about 450 hours that was a replacement for a damaged Lehman 120 by the previous owner.* When I bring the throttle to idle after a couple of hours of cruising, the engine will stall.* This doesn't happen*every time*but usually at the most in oppertune time.* Today.....rain, wind, narrow curvy channel!!!!!!.....NOT a fun situation.* Got set against the rocky channel walls before I could restart.* No damage other than a little scrape above the waterline on the black bottom paint.*

Anyway.....Is there an adjustment to the throttle linkage that I could make that will keep the engine from idling too low and quitting?*** (The usual idle is about 650 to 750.)* This stalling happened one other time when I pulled back to idle rather quickly, so I have been careful not to come to idle too fast......until today.* Somehow I have to find a way to keep it running.* Other than this stalling situation it starts and purrs like a kitten.* Any ideas?

Yes. Call American Diesel and ask for Bob or Brian Smith. It's their engine, they will know the possible causes and cures.

There should be a hard stop on the throttle linkage.

Did your engine come with a book?

Go down to the engine and observe the throttle linkage and have someone else move the throttle forward a bit then back all the way. You should see it contact the idle adjust device.

R.

For those interested......FYI, I spoke with Brian Smith of American Diesel today about the idle and quitting problem. The idle should be between 700 and 900 RPM for this engine. When I would bring the throttle to idle it would go down to 500 to 450 and then quit. We located the throttle linkage idle stop stud and are in the process of "breaking" it loose. It has not been adjusted for several years and is set up pretty tight. Not much room to get a wrench in behind the injector piping to loosen the lock nut and the put a long screwdriver on the end of the stud to make the adjustment. In the process of "breaking" it loose we broke half of the slotted end off the stud. (NOTHING is easy!!!!) We put a jamb nut on the stud and with a good spray of liquid wrench it will hopefully get moving tomorrow.

Another interesting thing that has been happening with this boat is that when we would return to the dock after a few hours of motoring around, the stbd. fuel tank would be almost full while the port tank would be about a quarter full. (I have site tubes) Come to find out from Brian, the American Diesel will return 10 to 15 gallons of fuel per hour back to the tank where-as the F120 Lehman that it replaced would only return 4 to 5 gallons per hour. The original Marine Trader was plumbed to return the fuel to one side and let the cross-over pipe move the fuel to the other side. Since so much fuel is being pumped back to one side only, it is filling up the tank too fast and the cross-over piping doesn't transfer the fuel to the other tank fast enough to keep them equal. The best thing it seems would be to plumb the tanks to refill equally but that wasn't done originally and may to be hard to do now. What has to happen is the fuel has to be drawn from the tank that it is being returned to and let the crossover take its time to make things equal. We are closing the supply valve from the port tank that goes to the filter half way for now and will observe the site tubes and see how equal the fuel is after a couple of hours running. Any other suggestions would be welcomed.

At our cruise rpm of 1650-1700 rpm each of our two FL120s burns about 2.5 gallons per hour.* Maybe a little less.* What you're saying-- or were told--- is that an FL120 returns 4 or 5 gallons an hour.* Doesn't burn it.* So that implies that the fuel lift pump is delivering something over 6 or 7 gallons per hour to the injection pump.* Of which the engine burns 2.5 and returns 4 or 5.

I have no idea if those numbers are accurate.* I've been under the impression that an injected engine burns much*more than it returns, but no matter.

The fact is that the engine is still returning less fuel that it's taking out.* So if you're making fuel in*a tank, it's only because that tank is not feeding the engine but it's getting the return fuel from the engine.

While your fuel return setup seems a little odd to me, the crossover line should in theory allow the tanks to equalize.* But only if the boat is in lateral trim when you're running, and only if the crossover line is not plugged or partially plugged.* If the manufacturer of your boat decided to let the crossover line compensate for the fact that the engine was set up to return fuel to only one saddle tank, I would have thought they would have had the sense to put in a large enough line.* Hard to believe your boat's been running around with this problem all its life.

It's possible the line is too small for the volume of fuel it now has to transfer from the newer engine.* Or it could be large enough but the line has gotten plugged or partially plugged, perhaps with gunk and sludge*that's collected in the tanks over the years and has gotten into the line.* Or if there are valves on the line, perhaps they are not functioning properly.

If it was my boat I would set it up so the engine returns fuel to whichever tank is feeding it.* If the engine feeds from a Tee in the crossover line (which is not a smart setup by my way of thinking) then the fuel should be returned to both tanks together or perhaps to the crossover line itself (but I'm not sure about that idea).

If you determine that the crossover line is not gunked up and that any valves in the line are working properly, the simplest solution is probably to replace the crossover line with something that can move a higher volume.

But a setup that allows the return fuel to go only to one tank is rather limiting, I think.


-- Edited by Marin on Friday 10th of September 2010 12:14:45 AM

PB Blaster or Kroil should be on every boat for loosening frozen nuts and bolts. Best stuff I've ever found for that. Auto parts store.

Marin, the Lehmans return very little fuel compared to what they burn. I don't know the exact numbers though.

Marin wrote:"But only if the boat is in lateral trim when you're running, and only if the crossover line is not plugged or partially plugged. "
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Even if the crossover line is clear, if the boat is not in lateral trim, there will be a difference in level between the 2 tanks.

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-- Edited by SeaHorse II on Friday 10th of September 2010 11:21:48 AM

"here-as the F120 Lehman that it replaced would only return 4 to 5 gallons per hour."

Let me clarify this for you.
Bob Smith is on record that the Lehman 120 engine returns "1/2 pt in 10 hours". Its almost zero return. I was with Bob when we ran one in the parking lot and no return line was even connected to any tank, Nothing came out.

I know Brian Smith and believe his knowledge of the 120 is more than sufficient. In fact he is quite expert about that engine. I suggest that perhaps there was some kind of communication misunderstanding about this 4-5 galls/hour return rate.
R.

A little clairification....Brian only said that the American Diesel will return 10 to 15 gallons per hour which is considerably more than the Lehman 120 hence faster and more fuel returned to the tank......My mech said he thought the Lehman 120 returned only about 4 to 5 gallons per hour.

reefdrifter wrote:

A little clairification....Brian only said that the American Diesel will return 10 to 15 gallons per hour

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Boy, that sounds like a lot.**The current AD engine is*150 hp, NA, and is (I think) a marinization of a currently*manfactured*Ford of England*diesel.* I don't know for a fact that the base engine is a Ford, however.

But I find it hard to believe that an engine so similar in power would return such a huge amount of fuel compared to the FL120, which is "only" 30 hp less.* Unless the differences in Jurassic-era injection systems and modern injection systems is pretty radical.* That's a question for RickB I suppose.

But 10 to 15 gallons an hour*return vs. 1/2 pint in 10 hours---- that's an amazing difference for such a modest increase in power.

I suspect a fuel system component manufacturer could return as much to the tank as they wanted. I wouldn't think HP would have as much to do with it as the desire for another result. Possibly dissapating more heat for longer shaft seal life or maybe the wear life on the injector pump, etc. is increased with a longer operating temperature? Certainly a benefit would be the stirring of the tank with that much flow me thinks

Lower operating temperature sorry- iPhone/autocorrect!

While I have no experience with either of the discussed engines, our old Volvo 90 HP engine returns enough fuel to the tank that it causes a steady stream from the return line into the tank. I know about this as early in our "life" with the engine at idle I could hear "water" running - took me a while to figure out it was the return line to the fuel tank causing an echo in an almost empty tank. Originally the set up was much like Reefdrifter described and if you were not careful you could over flow the starboard tank (single tank return) while drawing from the port tank WHILE AT AN IDLE AT THE FUEL DOCK - now don't ask how I found that little tidbit out In our case the balance line was free flowing and 1/2 inch diameter but it could not keep up with the engine return volume when the tanks were full or close to full. Volvo states this large fuel flow is used to cool the injectors !!
My solution was to replumb the fuel lines via a Groco 2 way dual fuel valve - switches supply and return with one lever - and solved all the grief.
Much as it seems like a rather stupid way of setting up a fuel system I have seen many such systems in vessels that I have been aboard so it is not an uncommon way of doing things.
John Tones MV Penta
Sidney, BC

You need to know your engine. Yeah, I know, sometimes that is hard when documentation is scarce from PO. Many return very little to the tank, many return a lot which has caused vent line overflows into the water.

Mine is a case. At full power it is RATED to burn 13 GPH, but the system will move up to 90GPH returning 77GPH to the tank. This relationship remains even when I plug along at 2-3 GPH. Detroits are another one that return a lot of fuel.

The excess is used to cool the injection pumps and injectors. On some engines a fuel cooler is added although usually this is only on high output engines.

Anyway, it's good you caught the change before you had an overflow.

You should be able to rig a return line to the other tank but you may need to consider a couple of valves to force fuel to go to the correct tank. It may not go where you want it to go. Just be sure you CANNOT completely close off the return path or you can cause immediate and expensive damage to the injection system.

On mine it took me a while to adjust properly so I retain a semblance of balance. My engine draws from both tanks always, so I fiddled over a period of time, to get a more or less balanced return. Any remaining imbalance is taken care of overnight through the crossover draw line.

Thanks C lectric and all.....
For now I am going to fuss with the valves as you did. I think I can monitor the return flow to the stbd tank and pinch off the port tank so it does not supply fuel as fast as the stbd tank to a point that it will balance out overnight. If I go on a long cruise and need more fuel from the port tank a little faster, I can open that valve and use that fuel while still returning to the stbd tank.

Had I known when my new tanks were being fabricated how the fuel was being returned and the quantity of fuel returning to one tank I could have had the port tank plumbed for a return line. Now it is a bit more involved drilling and plumbing with fuel in the tank. That will have to wait. I guess I could plumb a return line into the vent piping to that tank but I am not sure that is a real great idea.