Ford Lehman 120 idle speed not responding to adjustment

[socalrider]

My starboard FL120 is idling at 850-900 rpm; trying to bring that down to 600-700 to match the port engine. I have the Simms injection pump with the idle screw adjustment (versus screw/locknut stops on the control cable for some older versions).

I’ve started them up, let them settle, backed out the surge damper screw, then loosened the locknut and adjusted the screw on the idle speed adjuster. To no discernible effect on either engine, either way.

Any ideas what I’m doing wrong?

I loosened and removed the Morse cable to make sure it wasn’t the culprit.

One other potential clue: I just re-plumbed the entire fuel system, changed and bled the filters, and removed lift pumps, replaced with Warboro units. I don’t remember idle speed being this high before.

 

[kchace]

I ran into the same issue on my 135s, the throttle cable will also adjust the idle. You may have to adjust that as well.

Ken

 

[socalrider]

I ran into the same issue on my 135s, the throttle cable will also adjust the idle. You may have to adjust that as well.

Ken

Thanks Ken - I briefly disconnected the throttle cable (side note: what's its proper name on a diesel since there's no throttle?) to see if there was any residual tension - to no effect.

 

[SteveK]

.....

One other potential clue: I just re-plumbed the entire fuel system, changed and bled the filters, and removed lift pumps, replaced with Warboro units. I don’t remember idle speed being this high before.

Thanks Ken - I briefly disconnected the throttle cable (side note: what's its proper name on a diesel since there's no throttle?) to see if there was any residual tension - to no effect.

Interesting. Are you thinking the warboro is bypass the injection pump with the higher pressure input?

 

[socalrider]

Interesting. Are you thinking the warboro is bypass the injection pump with the higher pressure input?

I don't know - that shouldn't happen - the Walbro puts out 6-8psi, about what the mechanical lift pumps should have put out. I also used to have a pair of Carter electric pumps that would run in series with the lift pumps (also 6-8psi) before i re-plumbed.

 

[SteveK]

I don't know - that shouldn't happen - the Walbro puts out 6-8psi, about what the mechanical lift pumps should have put out. I also used to have a pair of Carter electric pumps that would run in series with the lift pumps (also 6-8psi) before i re-plumbed.

I agree it should not, just checking.

For what it is worth I needed to add 100 rpm and it was very touchy there at the bottom. I too disconnected the diesel acceletron (throttle) until I found my target idle.

 

[socalrider]

I agree it should not, just checking.

For what it is worth I needed to add 100 rpm and it was very touchy there at the bottom. I too disconnected the diesel acceletron (throttle) until I found my target idle.

Thanks - so you successfully adjusted with the idle screw? Mine didn't seem to do anything. Hmm... do you remember which direction slowed it down (in or out)?

 

[rgano]

Are you using a photo tach or depending on installed tachs?

 

[SteveK]

Thanks - so you successfully adjusted with the idle screw? Mine didn't seem to do anything. Hmm... do you remember which direction slowed it down (in or out)?

clockwise increases, counter decreases. Oh and I ended up loosening completely and then rocking the lever back/forth, perhaps paint or crud was the touchy part making it sticky in that position. good luck

 

[SteveK]

Are you using a photo tach or depending on installed tachs?

Rich, if you asked me.
I relied on my ears and then had a look at the installed tach. It was idling lower than the other one so balanced them

 

[socalrider]

Are you using a photo tach or depending on installed tachs?

Photo tach

clockwise increases, counter decreases. Oh and I ended up loosening completely and then rocking the lever back/forth, perhaps paint or crud was the touchy part making it sticky in that position. good luck

Thanks. Maybe I'll try backing it way out and see if that makes a difference. Will also play around with the lever.

 

[socalrider]

Photo tach

Thanks. Maybe I'll try backing it way out and see if that makes a difference. Will also play around with the lever.

Update: I backed the screw all the way out and still no difference in engine idle speed. Backed out the idle damper all the way as well, and no difference there either.

I pulled the cable off the "throttle" lever again as well and played around with it a bit - if I push it against its internal stop, the speed does drop down to 500-600rpm, but it's tough to get it to stay low unless I maintain some pressure on it.

Let me know if anyone has ideas. I'm out of things to adjust. Anyone have an idea why the idle speed adjustment screw wouldn't work? Internal diagram of the Simms pump?

 

[SteveK]

Idle adjustment, you probably have this.
The only other thought is change the oil, ensure correct fill and try again

 

[socalrider]

Idle adjustment, you probably have this.
The only other thought is change the oil, ensure correct fill and try again

View attachment 118718

That’s the one - no adjustment on the stops. I just changed the oil; filled until it came out of the fill level port - pretty hard to overfill. I did use 10-40 and have seen 30wt recommended since. Hmm…

 

[catalinajack]

The ends of my throttle cables are threaded. On them are spring-loaded ball stud keepers which attach to ball studs mounted on the throttle levers on the pumps. I adjust the idle speed by screwing the keepers in or out as needed. I have no idea whether this is the "proper method of adjusting idle speed but it works for me and it beats hell out of messing with pump adjustments. I have put over 1,000 hours on these engines and have needed to adjust the idle speed just once, early in ownership. It has been awhile but, as I recall, my adjustments were no more than three or four turns on the threaded cable ends with plenty of adjustment left.

 

[catalinajack]

That’s the one - no adjustment on the stops. I just changed the oil; filled until it came out of the fill level port - pretty hard to overfill. I did use 10-40 and have seen 30wt recommended since. Hmm…

The pumps on 120s take 16 oz of oil. No need to remove the upper plug until oil flows out. Just drain and refill with 16 oz of oil.

 

[socalrider]

The ends of my throttle cables are threaded. On them are spring-loaded ball stud keepers which attach to ball studs mounted on the throttle levers on the pumps. I adjust the idle speed by screwing the keepers in or out as needed. I have no idea whether this is the "proper method of adjusting idle speed but it works for me and it beats hell out of messing with pump adjustments.

Yeah, that's how all my previous motorcycles and gas engines worked. But this version of the Simms pump doesn't have any studs mounted on the throttle levers - the lever can't be let back any further; it rests on some internal stop.

The pumps on 120s take 16 oz of oil. No need to remove the upper plug until oil flows out. Just drain and refill with 16 oz of oil.

Thanks - good tip. Was a messy job!