Rich or lean during warm up?

[jedwards]

I am trying to work out if my WRD is set excessively rich or too lean during  warm-up.  The split test tells me nothing because it is meant to be running richer than usual in order to overcome higher friction during this phase, so how much is too much?  The WRD had two oval shims when I bought it, and I have removing both in an attempt to lean it off.  The CSV is good and pressure seems OK. The exhaust seems quite sooty during warmup but runs really nicely with the correct mixture at hot idle. Timing is according to Dr Benz with everything new.
It starts OK (CSV working properly) but seems  to stumble quite a lot during this first minute or so, and will even stall unless I am very careful with the accelerator. 
I believe I have the BC setup OK so it comes back to the WRD, but as I am down to zero shims, I am out of adjustments if its is in fact excessively rich.
How can I tell for sure?

Jeff


 

[Cees Klumper]

What happens when you re-insert shims, does the hesitation/stumble get worse? And have you checked the CO on the warm idle?

[w113dude]

On a cold engine WRD puts out more fuel, so if you are set rich you will be running even richer therefore uneven.
I would first look in to your spark plugs and see how they look, this is the best indication of your combustion rate too lean or too rich,
Then do a split linkage test on 2000 and 3000 rpm,  this will give you more of where you are in driving ranges, chances are you are running rich in all ranges and don't feel it as much when driving, if you still find you are too rich then take some shims off of the BC to bring you within range then try and adjust your idle speed with the thumb screw behind the FIP, I had a similar issue last week and this is the way I was able to resolve it.

A reve, counter and a CO meter helps a lot with this task.

[ja17]

Hello Jeff,

Yes, the split linkage test can will tell you the condition of your mixture even when cold. More fuel is required to counter friction, which results in a correct mixture for that temperature.
If all the oval shims are removed and the cold mixture is still excessively rich when cold, you may have to make a adjustment at the BC or main rack. Do the split linkage test during warm up and tell us what  you find. Make sure your engine linkages are adjusted correctly.

[jedwards]

Hi Ja17.
I did the split test during early warm up as you suggested and more air does increase RPM substantially, from which I deduce excessively richness. Yes, all the oval shims from under the WRD have been removed in an attempt to lean it off and I have 1.5mm of rounds shims under the thermostat. I also have ordered a new WRD thermostat  just in case. 

I have the BC set about right for smooth off-idle warm running, but if I lean it off (remove a shim, count the turns and screw it in further) during this warm-up test , RPM do rise slightly.

The other complication that might be impacting on the entire starting process is (what i believe to be anyway)  faulty IP ball valves. During cold-stat, I have to crank the car for at least 5 seconds before it starts to catch. The CSV is working OK, but I think I have to crank it for a long time to get the fuel to the injectors. The fuel pump sound does into indicate loss of pressure in the tank feed lines, so I assume it must be in the injector supply lines from the IP.  Is this likely or does long cranking usually mean something else?  Once it catches it stumbles and hesitates for first 30 seconds , then settles to what seems to be an overly rich mixture until it gets warm.

Could these be related? Can the IP check valves on an early 250SL simply be cleaned and lapped?

Sorry for so many questions but this is proving  really frustrating.

Jeff

[ja17]

Hello Jeff,

The engine should still start quickly cold. Check to make sure that the small fine  screen in the intake fitting of the Cold Start Valve,  on the intake manifold, is clear. Remove the metal line and unscew the fitting. Clean the screen then make sure that the CSV valve and solenoid work correctly during cold starts. Next make sure that the enrichment solenoid on the IP is activating whenever the starter is engaged. If the cold starting devices are all working correctly, the engine should start quickly after the ignition key is on for two or three seconds. It the engine stumbles, stalls or misses after the initial start, then you may have some other IP or injector issues. 

As far as the injection, you saying that it is still rich cold with all oval shims removed. You may need to make a full range adjustment by reducing shim height at the BC untill all is a bit lean. You can then go in and richen areas as needed by adding shims to the WRD, turning the IP thumbscrew and range screws. Proceed with caution. These are more advanced techniques. Record where you came from in case you need to return.