Warm up Enrichment

[Steven A]

Hi to all

A question.....is there any tuning/control on the period of warm up enrichment (this is for a 1964 230SL)?    I have the idle set up nicely with fully warm engine, very smooth launch.  Idle speed 650 to 700.   With cold start, all good...maybe 900 rpm reducing as engine temperature increases.   Problem is when up to temperature (on the dashboard gauge) no enrichment, and engine can tend to cut with very low idle rpm.

Whilst I can bump up the idle speed (slightly richen) to assist here, was wondering if there was any control over the warm up enrichment.

Thanks

Steven

[Cees Klumper]

Hi Steven - no answer for you, but just to say I have the exact same problem. What's more, I didn't use to have it, it started out of the blue a couple of years ago. So looking forward to finding the solution, hopefully through this thread. I have tried changing idle mixture, ignition timing, adding an oval shim to the WRD, all to no avail.

[jedwards]

You can adjust the cut-off point for your WRD. Yours obviously starts out OK but closes too early and before the motor reaches the right temperature.  Some time since I did mine but I recollect that the cut off time is adjusted by adding or subtracting round shims to WRD. .There is lot of really detailed instructions in the forum on this subject so search for WRD and take a look at the details on this subject on the Tech Manual.
Good luck

[Steven A]

Thanks for suggestion.

I have looked up technical manual (there is more discussion on the threads....as to whether the round, or oval, shims influence mixture above 1500 rpm)

May I confirm the round shims are #10 in the attached picture,

With thanks and regards

Steven

[jedwards]

There are a lot of experts in this Forum with vastly greater experience than my own, so please jump in if I am not entirely correct.

The shims you need to adjust are #6 on the diagram.  #10 are the oval shims under the WRD that alter the cold set mixture alone. Your problem sounds more like your WRD is shutting off too early, as that is controlled by #6 shims.

The WRD is basically a heat operated valve. At cold, the thermostats is at its shortest. As a result the air value rides high (open) in the body and the WRD's rod applies little downward pressure on the FIP rack, thus allowing it to run rich when cold. Yours is clearly OK at this point. As coolant warms, the thermostat expands, pushing the air value down (stating to close) and the rod pushes on the FIP rack to reduce the level of cold enrichments. The cut off point for the air value and the temperature at which enrichment slows or ceases is determined the number of small round washer-like shims between the thermostat and air valve.
In theory, once the motor is at running temperature, the WRD is fully extended and should exert no influence on external air or enrichment.

In your case, it sounds like you need to remove round shims from under the thermostat (rather than oval shims under the WRD) so that the WRD is active over a greater temperate range.
The way I did this was to remove the WRD from the car and blow through the vacuum port. If you air valve is working properly and is free to move, air should flow reasonably freely. Then drop the entire thing into hot water and retest at various temperatures to determine at what point the air valve fully closes.  I forget the exact temperature, but that will be in the Manual, but something close thermostat temperature would seem logical. Then you adjust the number of round shims until you have it fully open when cold and filly closed at the correct temperature.

HOWEVER, be aware that such changes will/could alter your mixture a little so your final step will be to reset your cold stat and warm running mixtures, either by adjusting oval shims under the WRD or via the FIP mixture control. Its fiddly to get right, but once you have it, it works amazingly well.

Good luck.

[alchemist]

I aqree with Jedward, # 10 in the schematics is not the round shims. They are either #5 or 6, exactly underneath the thermostat plunger. I hope this helps.

[Cees Klumper]

Thanks Jedwards and zalsaigh - no. 6 is what I thought. I also read up in the tech manual this morning and found much more relevant info in the forum threads. Will adjust the #6 shims and report back (and maybe finally decipher wiki language so I can add the info to rhe tech manual).