Steve--Regarding my 75 too rich 450slc. Using your advise and a gas analyser, My car passed the California Smog test with Flying colors. Of coarse I promply went home and richend the mixture up. Any Advise on what a good idle and off idle fuel mixture would be.I have sinced been warned that the afterburners run almost 300 degrees hotter when set to Calif. emission specs. MANY THANKS JOHN MILHOUS.

The two keys to power and efficency are timing and manifold vacuum/manifold vac sensor range.

The settings I gave you should have been fine for the non corrected map sensor mixture. (this is arrived at by disconnecting the throttle switch and deactivating the AIR pump). If it doesn't have power at 1% CO then you probably have lost range. If running it at 2-3% CO fixes the problem you will suffer a 5mpg loss of efficiency. When those cars were new I used to set the timing up and set the uncorrected map to .5% and then set the idle corrected mixture to 1%. I had many people getting 20mpg when those cars were new and the sensors had full range and the engines had maximum manufold vacuum.

I usually set the idle CO on the control unit to 2-3% CO.