You can't gain much in the way of fuel economy by
leaning the jetting - lean-misfire will set in and
your mileage may actually worsen.
The factory combinations are nearly ideal, just be
sure you have the correct air correction jet (and
corresponding main jet) for your application.
With a 70Z or 75Z A/C you should have a 127.5 main
With an 80Z A/C you should have a 130 main
With a 60Z A/C you should have a 125 main.
Generally you would run a smaller A/C in a heavy
vehicle (like a bus) and a smaller one in a light car.
A smaller A/C tends to richen the mixture out at the
top end, making it less risky to use a smaller main
jet. Depending upon what kind of driving you do, you
MAY be able to help MPG by juggling the combination,
but don't depart too radically from the
above-mentioned factory settings. Same goes for the
idle jet - in most cases a g55 is best, but stepping
up to a g60 could actually improve your mileage by
allowing you to reduce the main jet size slightly (if
your driving all consists of putting about town).
You can adjust the volume of the accelerator pump shot
on a 34PICT. Reducing it will improve your MPG at the
expense of driveability - it depends upon how much of
a hesitation on acceleration you can tolerate. Too big
of a "flat spot" could be unsafe some day when you
need decent response to avoid a hazard, so don't go
overboard on this adjustment.
Dual-ports are especially susceptible to hesitation on
acceleration because their intake manifold
cross-section is too large to provide good flow
velocity at low speeds - this puts conditions inside
the manifold closer to "dew point" so that when you
open the throttle and vacuum decreases fuel tends to
condense on the manifold walls. This causes a
momentary lean condition...the fuel does get to the
cylinders eventually, but it's in the form of droplets
which are too large to burn completely. Keeping the
manifold warm reduces this tendency, so the proper
function of the preheat system is important. Compared
to the stock muffler, no aftermarket exhaust system
provides near the preheat flow. A properly-functioning
thermostatically-controlled aircleaner and warmair
pickup system contributes to driveability; with a
single carb and a header I'd consider it mandatory.
Lastly, you will (theoretically) get better mileage
with a stock distributor that has both a centrifugal
and a vacuum-operated timing control system than with
a centrifugal-only distributor like the 0 231 178 009.
The stock distributor can respond to load as well as
RPM, allowing more total spark advance at high
speed/light load (highway cruising) which will improve
mileage. In addition, the stock distributor provides a
little extra advance off-idle compared to the
centrifugal type, which helps to fire a lean mixture -
driveability will be better without having to resort
to dumping excess fuel (the usual "answer" to the
flat-spot problem).
--- Damon & Gay <[EMAIL PROTECTED]> wrote:
> Does anyone have any recomendations for carberator
> jet sizes? For example, In the main or any others
> that might help fuel economy
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