I started tweaking the AFC on my '85  1.9l Digijet on Saturday.  I tied in
the voltmeter to read what the O2 sensor is feeding to the FI.  I started
by moving 4 notches leaner (clockwise).  It made very little, if any,
difference in the performance or the O2 sensor output.  I then moved it 2
more notches and disconnected the O2 sensor from the system and fed it
directly to the voltmeter.  It runs leaner with O2 sensor on-line, so the
ECU is doing something to adjust the mixture.  I'll take this as a good
sign!   I then went 2 more notches for a total of eight.  I am going to
leave it there for now.  It seems like the ECU will adjust the mixture to
whatever it wants.  The only way to set the mixture would be to run open
loop (O2 sensor disconnected) and continue adjusting down on the AFC
spring.  At some point, the spring might be too tight and affect the off
idle response?

                                                        Jay