I have a 1975 1.8 (L-jet) with all the cat stuff removed.
The car runs strong (I believe), I can reach 110 mph.
But when driving slow I get bad mpg (about 20 when other achieve 30) and my exhaust has black dirt.
I suspect my car is running too rich. Can this be the cause of bad milage ?
When I let the car checked they found 0.8 CO. is this OK ?
How can I test, fix, improve, ajust ?

I would suggest maybe if that rich 8.0 co. Anyway maybe the flap in the air flow meter is sticking. That would certainly cause the low speed problem. Check it when the car is very hot and everything in the flow meter has expanded. Pry off the top and check the spring loaded pointer. If it sticks or squeeks that is the problem. If the fuel pump runs constantly when the key is turned on that is an indication that the flap is sticking as well

When I say "low speed" I mean 50 60 mph. I should achieve 30 mpg at theese speeds.
I tested the key. Seems OK. Pump doesn't run until the engine runs.

Have access to a AFM like a LM 1 meter? I adjusted my Ljet Westy using one to set the AFR to 14.2 to 1 under load at 2500rpms.

To adjust the AFM you pop off the cover and loosen the little screw and move the wiper ever so slightly and retighten. When you are done you must check the pump shutoff arm and readjust that too so the pump shuts off when the wipe is a rest.

I can post of pic of the inside of the AFM if you want.

this may help !

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Wow high speed man! I would put a probe in the pipe and check the air to fuel ratio at that speed

here

very cool. saved that picture and text.

k

Thank you ! this is very helpfull.