[Amc-list] Air Fuel - Leaner

[JOE FULTON <piper_pa20@xxxxxxxxxxx>]

Today I used the wide band oxygen sensor (Innovate
brand instrument) to adjust the BBD carb on my 77
Gremlin.  The car runs good, but was getting only
about 13 miles per gallon with a tune-up to specs on a
60,000 mile 258 engine.  And a factory rebuilt carb.

The first readings, with no carb adjustments showed an
Air/fuel ratio at about 10.9 to 11.2 at cruise
throttle settings.  I couldn't get my dwell/tachometer
to work with the electronic iginition so I have no
actual rpm readings.  At idle the A/F ration settled
to about 16.5 to 17.0 to 1.   Lean settings at idle
are OK I think since the engine is not developing
power.  And it was a good indication that the idle was
set slow enough that the idle circuits on the carb
were definitely engaged.

I fiddled with the carb for awhile, trying to lean it
out using the instructions from the Mopar slant six
web forum.   These instructions turned out to be
useless.  I don't know how these guys adjust anything
except by ear.  There must be a lot of poorly tuned
slant sixes running around.

Anyway, after trying for two hours or so to decipher
the printed directions I had downloaded I went to
Kragen's and bought a carb kit for my BBD, just for
the directions on tuning the carb.

After returning everything to the instruction sheet
settings except for one thing which I'll explain
below, the Air fuel/ratio fluctuated from about 12.6
to 1.00 up to 13.1 to 1.0 at cruise rpm.  That's in
the target zone I think.  It's still richer than
stoichiometric, but nothing is perfect in the real
world.  I hope to see some improvement in miles per
gallon on this car.  

The exception I mentioned above is a small allen screw
on the vacuum piston assembly. This screw is not even
mentioned in the carb rebuild instructions. The
setting on this screw microscopically controls the
depth of the float rods into the jets and thus the
air/fuel ratio.  I messed with this screw and could
not determine the factory setting for it.  Based on
the readout from the Innovate, I think I got it close
to the factory setting.

Joe Fulton
Salinas, CA     
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