Bob,

'71 is a year-only MAP sensor in the 140; not the same as '72-'73. However, the only difference is the calibration, AFAIK.

Let me review the "plugs a little dark" thing again. Plug color doesn't tell you anything useful about mixture. If it's too rich, not all the fuel will burn and the result is soot. Soot is black, period.

The place to read mixture on plugs is the center insulator. If there is soot all the way to the electrode, it's running disastrously rich. If the soot starts partway down the insulator leaving a clean area around the electrode, it's quite rich. Best power comes from the mixture that's just barely lean enough to erase the last little ring at the bottom of the insulator.