Steve,

Much MUCH appreciated. I am really pleased that I am on the right track- since you have done this before, although in a much more controlled manner.

When I said that I would disconnect the frequency valve, I did mean electrically, not physically, so we are on the same wavelength on that; stopping active mixture control. I wish that I could check the CO of each cylinder individually, but…oh well.

About your ‘differential flow analyzer’ – Maybe I can obtain 8 graduated beakers and perform that test. I will not have the special screw to hold the air flow meter in place, but I can mickey-mouse something to function in the same manner. I would then time the flow with a stopwatch to obtain approximate flow rates of 10, 35 & 60 cc per minute. If I understand you correctly, if the 10% differential at ALL of these different flow rates cannot be maintained, then the fuel distributor is beyond adjusment?

And out of curiosity, in your experience, what may have caused the calibration to drift in the first place? Or is it just a matter of time & mileage? (about 250,000 miles so far, and still plenty more to go )

Thanks again!