Throttle Creep?

[Capt. Rodbone]

Another question our adventure has led me to. I think I’ve heard it referred to as throttle creep however a search online didn’t lead me to any information. My excuse for not searching the archives here for some knowledge is we are currently underway but here is my question.

The score on our journey of about a week our sweet spot seems to be 1500 RPMs with our twin Lehman 120 engines. Today they don’t want to stay at 1500 RPMs. They want to settle in at about 1250 unless I keep pressure on both throttle handles. It is interesting and there is likely a reason why both seemed to be affected simultaneously. I suspect these screws I see can play a role in the solution however there are four of them, two on each throttle handle and two on each housing but the last thing I want to do while traveling is experiment on something.

As always I look forward to the knowledgeable responses I will get!

 

[C lectric]

I can't help but to suggest we need to know which controls you have, Mfgr. name and model and a couple of good photos. THere are many different controls out there and that will/should help.

Maybe a couple of shots where the cables connect at the injection pump also.

There should be a pressure adjustment to create enough friction to hold a position.

 

[Shrew]

I once had a situation where I couldn't get the throttle to go past about 2000 rpm. It was like I was wide open throttle, only there seemed to be a lot more travel left. I went down below and found someone had placed something in front of the lower helm throttles that had slide and were effectively blocking the lower helm throttle.

Got through the entire path of the cables and make sure they're not get blocked or impinged anywhere.

 

[O C Diver]

Depending on tensioning settings, the throttles may be decreasing from vibration. While I have helped friends with their Lehman 120s, I'm not fully versed in their throttle controls. Most mechanically injected diesels have a spring that pulls the throttle towards idle (safety feature). The tensioning is mostly accomplished by an adjustment in the throttle controls at the helm. In the situation of upper and lower helms, generally only one helm has tensioning. In some situations the two helms and shifters are combined in the engine room. I have no idea how those are tensioned.

If you want suggestions on adjusting the tension, you will need to identify your helm controls. A picture would be helpful.

The other question is,"what has changed "? Generally motor controls (shift and throttle) are setup for each engine, not both throttles in the same control unit. Generally tension controls rarely change, and not both engines at the same time. Increased vibration can make throttles slip. Might be worth riding in the engine room for a few minutes at normal cruising speed to see if something has changed. A prop blade out of pitch, bent shaft, loose shaft coupling, bad motor mount, and worn cutlass bearing(s) are some of the more common vibration problems.

Ted

 

[Crux]

Sounds like a couple of 'cable brakes' are in order....they induce a drag which you adjust to suit....

Also, check your throttle return springs at fuel pump....perhaps they have been replaced with springs stronger than original, creating the problem


https://shop.sailboatowners.com/prod.php

 

[Crux]

I see that link didn't copy thru.....try this....or search Teleflex -Morse Cable Brake

https://www.jamestowndistributors.com/product/product-detail/9534

 

[O C Diver]

I see that link didn't copy thru.....try this....or search Teleflex -Morse Cable Brake

https://www.jamestowndistributors.com/product/product-detail/9534

Morse controls whether original or knockoff copies have built in tension adjustments. Clamping the throttle cable sheath to distort it and add friction is a poor idea that can lead to premature cable replacement. The tensioning adjustment in Morse controls work well once you understand the adjustment process.

Ted

 

[soin2la]

Based on age and engines, I’m guessing there is a high likelihood of Morse Tekeflex controls, as shown below.

Three of the screws are for a detent kit and the screw you need to play with is the bottom one on the lever, which adjusts lever friction.

If it is dual controls with both throttles on the same control head, you adjust only one screw because the two sides are internally linked. That explains why both engines slow at the same time and as noted, is probably due to RPM related vibration.

Make small quarter turn adjustments in one direction or the other and give it time to work, or not.

 

[O C Diver]

Based on age and engines, I’m guessing there is a high likelihood of Morse Tekeflex controls, as shown below.

Three of the screws are for a detent kit and the screw you need to play with is the bottom one on the lever, which adjusts lever friction.

If it is dual controls with both throttles on the same control head, you adjust only one screw because the two sides are internally linked. That explains why both engines slow at the same time and as noted, is probably due to RPM related vibration.

Make small quarter turn adjustments in one direction or the other and give it time to work, or not.

Ted

 

[soin2la]

Ted

Good find.

 

[Comodave]

Sounds like a couple of 'cable brakes' are in order....they induce a drag which you adjust to suit....

Also, check your throttle return springs at fuel pump....perhaps they have been replaced with springs stronger than original, creating the problem


https://shop.sailboatowners.com/prod.php

Our last boat had Lehman SP225s in it. The starboard engine had one of those on the throttle. I never messed with it, figured it was there for a reason.

 

[Capt. Rodbone]

Will adjust today

We are back underway and I will make slow adjustments to the bottom screw today. Sorry for the belated reply but the holidays and all……..
Hey I’m posting a couple of pics of mine. Again these are twin 120 Lemans original engines 1978 Grand Banks 42.

 

[Capt. Rodbone]

Thanks Folks!

If only all obstacles on a boat were this simple. Some of you pointed out which of the screws on the throttle handles I should’ve adjust and with just a bit of playing with it it will now hold my desired RPMs without issue.
Thanks again to all you fine folks.