Target co figure for higher revs

[Val]

Hi All

I am battling with the fuel mixture on my newly aquired 280sl. It would appear that most parts have been messed with by somebody that did not know what he was doing     I have now fitted the linkages in their correct places (two rods had been swaped), fixed the WRV that was locked fully open because the small bucket that takes the shims had been fitted upside down! I have set the valve clearances, set the timing etc etc. Everything is good at idle. Co is 4.2% at 750rpm and the WRV air intake shuts off at 70c. HOWEVER, as soon as I increase the revs above around 2000, the Co is up to 9.5%.

My guess is that the numpty that messed up the WRV tried to fix the situation by adjusting the Full Load Screw. The only problem that I have is that I can not find a reference for the CO at anything other than idle. Does anyone know what it should be at say 3000 and 5000? My guess is that it should be slightly weaker than the idle setting, but its a long time since i last played with this sort of thing so it would be nice to know for sure  

thanks

Val

[mdsalemi]

Just a hunch here...

Is it possible with all the monkeying around, that someone actually mis-adjusted the mixture?  If I am not mistaken (I have not done this so experts will have to weigh in here) there are some mixture controls that are hidden underneath a plate (they are hidden to prevent willy-nilly adjustments by people not knowing what they are doing?)  Perhaps you are now, too rich?

A tuneup man who WAS familiar with the FI system on my car DID make some adjustments like this...

[Benz Dr.]

That info is in the manual or BBB. It's not that much, maybe 1 or 2%. Mid range is much leaner than idle.

[Val]

Hi, Thanks for that. Any chance of looking it up for me? I only have the Haynes manual at the moment, and it has only the idle co figure.

Thanks

Val

[Benz Dr.]

The idle mixture value is nominal at 3.5 to 4.5% on all the pumps from R20 to R25 except R24w which is 2.0 - 3.5 at idle
Full load in 3rd gear 2.0 - 4.0
lower partial load 50KM in 4th gear 1.5 -3.0
upper partial load 100KM in 4th gear ( basic driving speed ) .2 - 1.5
R24w tends to run a bit leaner across all the ranges. If your engine stalls when put in gear it can be set higher for R24w up to 4.5% max at idle.

This could be done on a roller test stand as and E test. I think they do testing here at around 30MPH on the roller test stand. Modern cars will run .1%CO with cats so .2%CO is pretty good for these cars.
 As I suspected, our cars lean out a lot at road speed. Your main fuel ratio test should be done at speed and then quickly turn off the engine to pull spark plugs. They should be tan to brownish white but they could be redish depending on fuel additives in your local market.
If you see very bone white it's probably too lean. If you see the same colour and black spots on the plug it's so lean the piston is staring to melt. Anything black is too rich.

[Val]

Many thanks for the info. My BBB arrived this morning, so now I have more information than I know what to do with!!

However, interestingly, it includes details of how to test the CO without the use of a rolling road. Just need a vacuum gauge and 12v CO meter (both of which I have).

I am away for the next week, and need to finish a few jobs on the 280 when I get back, but as soon as I can, I will rig up the test gear and give it a go. I'll report back with the results.