<VV> Leaning Out the Midrange

[Brent Covey]

Hi Mike-

The first place to start looking assuming they are perfect shape carbs is
deactivate the Power Enichment circuit. When PE is active, mixtures drift
into the 12:1 range. pre'65's and AIR cars do not have a PE, and it can be
deactivated in non AIR carbs by changing the venturi cluster gasket to one
that covers the hole for the PE needle.

I have a theory on lean jetted 110 engines that a surge around 35-45 mph is
the PE circuit coming into play. I havent tested it but jetting
significantly richer kills the surging, and I think that might be why. This
might be whats happening to you. Normal GM carburetors operate at 16-17:1
mixtures during cruise, not sure if this is also true of Corvair but its
likely.You will be far out of range on your current sensor is thats the case
soon. It would be reasonable to presume at somewhere around 55-65 mph a
50-51 jet in an enriched style HV running the original high energy conntent
leaded fuels (as compared to reformulated blends or weaker winter fuels with
less BTU's per gallon) is supposed to be somewhere around that 17:1 mixture
originally. This is why most engines got better economy with the Quadrajets
than the TBI with O2 sensors in highway driving, all else being equal. The
PE circuit is the catch-all to cover your butt with lean jetting and adds
fuel back to hopefully mask the transistions when slightly greater output is
needed than lean mixtures could support. On 140 engines its virtually never
in play, and doesnt seem to open much before 100 mph. On 2 carb engines it
emerges from time to time.

Bear in mind running superlean will make the engine ping much easier, and
may eat your fuel savings quick by requiring higher octane and or reduced
ignition advance. I have generally found jetting slightly rich produces
better results overall with no deleterious effect on fuel economy, but will
be interested in seeing what your results are. With 52-53 jets most
110/Powerglides should be able to consistently produce 28 US mpg+ on 'real
gas' in conservative (55-65mph) highway driving using the enrichment carbs.

Good luck!
Brent Covey
Vancouver BC

> QUESTION: has anyone out there already ventured down this path?  What area
in the
> stock carbs is the most likely place to start in working on the  midrange
F/A
> mixture?