The knob on the outside of the ECU only affects idle mixture. You are supposed
to set it using a CO meter on the exhaust at idle. I turned mine all the way
down and it works OK.
I have a couple MAPSensors that have a hole drilled into the aluminum plug on
the end opposite the hose (usually covered by clear epoxy) - you can reach thru
there and adjust the mixture somewhat. Pretty hard to evaluate the results
though. If you could adjust it while under power it would be a lot better.
Maybe some long wires and a long hose... have a buddy do it inside the car.

Another way to adjust it is to add resistance either across or in series with
the coolant temp sensor. That is what the IPD adjustable ECU did - but it was
only for making the mix richer by putting resistance in series with the sensor.
If you put a resistance across it (should be a pretty high resistance - you
would probably want to put a fixed resistance in series with the pot you use
for fine adjustment so you don't make the engine think it has gone dry or
something) Use ohm's law and figure out with the curve in the manual what your
target resistance is and then calculate what the parallel resistor would be to
approximate that.
--
George Downs Bartlesville, Heart of the USA!