Idle fuel/air adjustment

[col320ce]

I'm trying to adjust the air/fuel mixture as per the last little bit of: https://www.sl113.org/wiki/Restricted/Linkage-tour and I'm having trouble with it.
Firstly the engine smokes like a chimney when you accelerate (it has done this since the cylinder head rebuild which was the first thing done when I bought it a few years ago).  The engine was rebuilt some time in the past (bottom end as well) but there was electrolytic loss of the aluminum due to a stray current so I had to do more.
I've adjusted the linkages, valve clearances (and they were pretty good since last time) and confirmed TDC is all lined up (I used a dial indicator gauge to confirm).
I've connected the vacuum to the inlet manifold (see photo) and when I adjust the air screw to get best vacuum I also get a very fast idle (1200-1400).  I've basically backed the screw on the injection pump all the way and I can't get the idle to go down (turning it anticlockwise when viewed from the driver's perspective).
I'm obviously doing something wrong but I'm not sure what it is ...
Any thoughts??
(64 230SL)

[WRe]

Hi,
what do you mean with "I've basically backed the screw on the injection pump all the way" ? There are a lot of notches to back anti-clockwise (>60) to reduce CO and it's only relevant for idling. At speed, the amount of fuel to be delivered is taken from the setting of the control rod and is - more or less - not changeable. Maybe your whole FIP has to be overhauled.
...WRe

[col320ce]

I can feel that I can no longer push the screw in to engage it... So that's how I know where I am. An overhaul is mega bucks I'm told and I'm guessing it's too complicated to do myself? More than happy to do it myself if it's possible... I'll do a search.

[WRe]

Hi,
some years ago we had a workshop with a specialist and the message was:"Hands off your FIP! You can't do anything without a test bench".
But these guys offer to check your FIP first for small money (~150€) to do a first analysis what's necessary.
...WRe

[col320ce]

That's not a bad plan... What's are their details?

[Pawel66]

I am not a mechanic, but I went through a similar process.

If your car produces smoke like a chimney on acceleration (I had the same thing after re-build), it may do so for some time and then stop - if it is burning out some of the assembly grease that might have found its way here or there. But if it continues and if your spark plugs are black - your car may be overall too rich. If this is the case, you will not adjust it with the thumb screw that is sticking out in the back of the FIP, because this thumb screw is for the idle only, works up to ca 1700rpm. The overall FIP has to be adjusted first, then the idle part of it.

There is another screw for the overall range of rpms adjustment. There are also screws for partial loads adjustments, but do not even think of touching them.

You have all that info in Technical Manual. There is also massive amount of threads about it on the Forum.

If something happened to the idle adjustment screw, as you say, it is a bit of a trouble to get to it in your type of the pump (as you have this big nut probably in the back, rather then the simple plate) and because indeed it would be good to adjust your FIP properly (before any re-build decision) - it is probably best to send it to try to check and adjust it. Hope the shop will be honest and will not try to squeeze $$ from you.

One other important point: do not even think of detaching FIP linkage lever from its shaft as you work on your FIP.

While putting back FIP into the car, you would have to pay attention to its timing.
 

[jeffc280sl]

are you speaking about the thumb screw on the back of the pump?  if its backed out too far you will not feel the clicks.   i have a spare pump that i can look at and provide inside pics

[WRe]

Hi,
you should contact these guys and ask for a first analysis:
- https://classic-manufactur-goslar.de/
- https://www.oldtimer-technik.eu/
Both are recommended by German Pagoda forum Pagodentreff.de.
...WRe

[Benz Dr.]

If you have your idle mixture screw turned all the way out ( or in ) and your engine is still running too rich the whole pump is probably running that way across all RPM ranges. In some cases it may be too rich at partial or full range but I start with the notion that I either have to add or subtract fuel. I turn the barometric compensator in or out until the engine idles smoothly and picks up throttle sharply. Before I  begin I always mark the top of the compensator so I  have a basic position for reference. Add shims ( out ) to make your mixture richer and remove shims ( in ) to run leaner. Generally speaking a big mixture problem usually needs anywhere from half to a full turn to cure. Your engine may not idle well after making this adjustment so you can tune with the mixture knob at the back of the pump.

Note:
compensator has to be completely removed to add or subtract shims and this is why you must mark your starting point before you begin. Aside from removing the compensator ( which can be really tight sometimes ) it's not that hard to do.     

[ja17]

Good info from Benz Dr. !

[col320ce]

This looks really easy!  And, after some reading, a failed BC would have the opposite affect of reducing the fuel (although I may as well bench test it when its out).
This topic was very useful: https://www.sl113.org/forums/index.php?topic=12175.0
Thanks again ... Update at the end of tomorrow!

[jeffc280sl]

good luck.  benz dr always offers great advice

[wwheeler]

If I am not mistaken, JeffC had the idea sometime back of jamming a rubber hose between the BC and the WRD tower to temporarily hold the BC in place while testing the car on the road. That way you can make quick adjustments back and forth until you get close. Then use the shims to finalize the setting. Mark the position of the compensator as the Dr. suggests.

Within reason, I always use the BC to adjust the total mixture and never mess with the screws in the back cover. It is just too easy not to use it. It is Very sensitive and even .003” can make a noticeable difference.

[Benz Dr.]

If I am not mistaken, JeffC had the idea sometime back of jamming a rubber hose between the BC and the WRD tower to temporarily hold the BC in place while testing the car on the road. That way you can make quick adjustments back and forth until you get close. Then use the shims to finalize the setting. Mark the position of the compensator as the Dr. suggests.

Within reason, I always use the BC to adjust the total mixture and never mess with the screws in the back cover. It is just too easy not to use it. It is Very sensitive and even .003” can make a noticeable difference.

I agree. Using the BC to adjust fuel mixture may not be 100% fool proof but it's a whole lot easier to keep track of what you're doing. Marking the BC before starting is the key to everything because you need that as a point of reference. 

[col320ce]

I removed the BC and the are two 2mm washers on it (total 4mm thickness) that have yellow paint on them. It looks to me that they were put on at the time that the pump was overhauled (there are yellow dots on the bolts holding it together too).
Before washer removal - about 1500 rmp, and to get best vacuum the air adjustment is screwed out a lot.
After removing one washer, the BC tightens up about 1.25 turns and the rmp goes down to about 1000 and the air screw is screwed in almost all the way (in fact it still idles well with it all the way in).  In this state the split linkage test suggests this is a good air/fuel mixture.  I'm assuming the average car has the air screw about half way which makes me feel whatever I am doing is incorrect and that I am now running super lean although I still can't get the idle rpm to lower.
And now ...
The engine idle drops after a while and the car stalls.  This makes me think that there is a 'cold start' mechanism that may not be turning off properly and that I am trying to tune the car in a 'choke' type situation.

I'm unable to take the car for a drive as it's chocked into my carport and it's a 2 person, 30 min job to get it out (and I have no friends during covid  ).

Any thoughts??

[Cees Klumper]

Are you starting the engine cold each time, and it stalls as the engine warms up? And your idle is high, but only as it is warming up but, once it is up to operating temp, does it then idle better/lower (beyond the 'window' during the warm-up cycle that it tends to stall)? There is a different set of possible issues during warm-up, compared to when the car is at operating temperature so it is important to know when your symptoms occur.

[col320ce]

I think the car is warm... I leave it a long time before starting the tuning. I make sure the top radiator hose is hot then let it idle another 5 or 10 minutes then start the procedure.
Once it is warm and I turn it off to make an adjustment I'm only waiting 20 seconds or so to make the next adjustment (it's only off for a minute or two.)

[jeffc280sl]

check out this thread.  take a pic of the bc stem and maybe we can tell if it has failed.

https://www.sl113.org/forums/index.php?topic=29130.msg210619#msg210619

[Cees Klumper]

What puzzles me is that the car starts to stall after some time idling when already fully warmed up. That should not be and whatever causes that condition may also help explain your idling mixture problem.

[Pawel66]

I had that and it was far too rich mixture.

When I had far too lean mixture, the idle was waving and stalled.

[col320ce]

I've done lots of reading and this is where I am up to:
Pulled the 7mm bolt from the CSV to make sure that there was no fuel leaking.
Put the BC back the way I found it with the 2 large washers and took some photos of it (from hex edge to tip is 21mm which should mean that it is good)
Checked the air line to the WRD is not damaged
Listened to the air intake on the WRD during start up ... there is good airflow but it does not turn off even when the car is "warm" (remember all I can do is rev the engine atm to warm it up.)
During cold start:
starts ok, revs at 800
the revs slowly increase to 1200 when the top radiator hose gets hot but are not really going beyond that no matter how much I rev the engine or wait
the split linkage test during start up gets a little bit more rev when adding air but this is minimal
WRD air filter sucks air and does not stop sucking air
there is an exhaust popping sound that gets worse as the car warms (not sure if this is pinging or not)
My Conclusion:
The car is either not warm so I can't tune warm idle
or
The WRD is malfunctioning ot at least should be turning off a little earlier.

I assume the next step is to pull the WRD and bench test it?
I have an early 64 230SL - I think this may have a bolt I can use to "turn off" the WRD ... can anyone ID the bolt from the photos (I've put a red arrow against my best guess)?

Thanks again to everyone

[ja17]

I think I would hook a fuel pressure gauge up and see what it reads when the engine starts popping. Sounds like it is fuel starved.

[Pawel66]

Just a voice from an amateur in case the fuel pressure test checks ok.

Does you temperature gauge say the car is warming up ok?

If it is sucking air when already warm, I think this may indicate WRD not working. So it is either not working in full (allows more of both fuel and air) or partially - shuts off fuel, but not air.

It is fairly easy to get a thermometer and a pot of water on the cooker and check if the thermostat is or is not opening as it should. You can do it with removed thermostat. You can also submerge assembled tower in hot water so that the thermostat housing is filled with hot water and try to blow air to see if the valve shuts off air in case the thermostat is working. Just lungs generated pressure is relatively small, bear that in mind.

I trust you went through WRD working and understand the oval and round shims topic.

Here is my struggle, car won so far: https://www.sl113.org/forums/index.php?topic=29221.msg212778#msg212778

[col320ce]

I've just pulled the WRD and bench tested it and it seems to be working.  It shuts off the air when put into hot water.  I managed to lose a round shim that flew through the air ... I'll try to find it tomorrow or assume it's 0.1mm and try to make another (I didn't measure it before it flew away).
So I'm either:
not getting the car to temperature
the WRD was stuck now it's fixed (it didn't feel stuck)
there is an issue with the water flow to the WRD.

I noticed a few comments that there was not much water in the pipes around the WRD when the pipes are removed.  I found the same thing to... I'm not sure if there is a possibility of an air trap here so I'll get the thermometer onto the WRD thermostat housing tomorrow after I put it all together.

[Cees Klumper]

In addition to Joe's suggestion on checking the fuel pressure, I would focus on making sure the air going through the WRD does shut off, otherwise I think you are getting false air throught it. The point in the warm-up cycle where it should shut off is not that long after cold start-up, certainly before the thermostat opens, I would think.