AFM Adjustments Yield good running but rich

[jlaudin]

Over the last month I have slowly and carefully tuned the AFM and now have a beautifully running bus, although a little "hot" (CHT at 380 at cruise). Yet paradoxically rich.

My question is, is there something inherent in the "BRAIN" that forces the Air Fuel ratio in our L-Jet buses to 12-11.8?

This is a 1978 2 litre stock fuel injection with ballast resistors.

No matter what I do, when fully warmed up and at 2400 rpm going down the road, I end up with a/f ratios just under 12, even with the cog wheel clockwise 6 clicks.

I have seen other's describe putting a resistor in line with the CHT 2 sensor to "cool" the engine, but don't know if that's appropriate here, or if I am missing something else.

Please advise.
Jeff

[Bleyseng]

inherent? no, just the way the AFM is adjusted. The small screw in the center of the wiper arm can be loosened and the wiper arm moved to lean out the mix. Small movements produce big swings in the mix so a LM1 meter is advised if you want to change this.
I run 14 to 14.5 to one at cruise (2500rpms up a slight grade)
Wide open throttle is 11.5 to one so yes, you are running rich.
The CHT could go down with leaning out the mix so I would change it.
Have you read Colin's AFM article?

[Amskeptic]

I run 14 to 14.5 to one at cruise (2500rpms up a slight grade)
Wide open throttle is 11.5 to one so yes, you are running rich.
The CHT could go down with leaning out the mix so I would change it.
Have you read Colin's AFM article?

14.5 at slight upgrade is ragged edge of lean.

Wide open throttle at 3,000 rpm should be 12.0-12.5. It WILL change at different rpms, and should slightly lean out as you get on up towards 4,300 rpm horsepower peak. This is NORMAL and expected as the volumetric efficiency of the engine drops.

CHTs rarely go down as a result of leaning the mixture, keep an eye on just how your CHTs respond to any adjustments you make. Let us know what you discover.

The article I wrote has to be updated. My linear brain has met up against the wily ECU's attitude problem with its infernal inner mixture map that is jerked around by the rpm signal. . .
ex. pushing the wiper rich at idle actually leans the mixture, wtf? ECU reads rpm signal and decides that the engine may flood.
Colin