My story:  My 85 westy automatic, with my old 1.9 engine with 150k
miles on it with low oil pressure, I'd get about 14-15 around town
and 17-18 on the highway, driving around 60-65mph.

I recently had a rebuild 2.1 put in (with new plugs, distributor, and
ECU) and now it seems like I'm getting around 12ish?   Of note, my
speedo cable seems to have developed a kink at the same time, and now
when going about 10-20mph the needle is jumping around and I can hear
it go click-click-click.    It also seems like the engine is running
rich, but I'm not sure about this.

Question -- could a partially damaged speedo cable be causing my
odometer to read wrong?  Or is it more likely that my engine is in
fact running rich with the new ecu, and i need a tuneup?