D Jetronic Question

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I have this on the tech and vintage forums, so thought I'd fish this pond too.

With the D Jetronic system on a 350 SL (US model, actually a 350SL 4.5), the underhood emissions tag shows the desired idle CO range to be 0.5% to 2.0% CO. It is a snap to set the idle at 1% CO and it runs great there.

Does anyone know what a well-tuned D Jetronic system should have for a CO reading in the cruise range, say at about 2,500 to 3,000 rpm? I have always heard that the cruise CO figure will improve from the idle figure because the engine is operating in a more efficient speed range. However, this car runs richer as the speed rises, with much higher numbers as the rpm climbs to cruise range. Measured CO at 2,500 is about 6.5%. Seems awfully darn high.

Other info: all new plugs, wires, filters, timing is right on, all injector hoses were preplaced, new exhaust, you name it, it was done at the last major ($$!!) service about 600 miles back. Sensors meter out fine, and no leaks from the start valve. Can't find any vacuum leaks either. Gas mileage is 12 - 16 mpg. Car runs like a top otherwise but there is soot in the tailpipe from the too rich mixture. Plugs show rich mixture around town, but quickly clean up on the road. Have used NGK BP6ES plugs for years which seem just fine. (Car did not come with a cat converter, it's a 72.) All other items are MB/OEM. Car has been relocated from California at sea level to 3,000 foot elevation. Again, car runs like a top.

So, is it broke, or just a thirsty devil?

Any advice will be greatly appreciated,

230/8