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Tuning for maximum
fuel mileage is fairly straight forward.
Simply install leaner fuel jets, and maybe
even larger primary air bleeds. But extreme
care must be used when setting the carburetor
extremely lean. The rotary will run cool at
cruising speeds at 2500 RPM with a lean jet
configuration, but if you begin to try to
drive it in the same agressive manner as if it
were jetted for performance, you chance
overheating the engine very quickly. Remember,
with jetting for performance or economy, you
can have all of one or all of the other, but
unless you are willing to sacrifice some
of each to find a compromise, you can
never have both.
Here again we have
the Sterling & stock Nikki base line
jet configurations for comparison. Note how
for the economy configuration, the secondary
main air bleeds are not all that large. This
is because the Nikki goes slightly lean up
high, and we need to ensure a fail-safe
against overheating.
|
|
Primary
Main
Fuel |
Primary
Main
Air |
Secondary
Main
Fuel |
Secondary
Main
Air |
|
|
Economy
Tuning |
.032
( smallest
) |
.027 |
.052
( smallest
) |
.048 |
Configured
for fuel economy. Very little
power, and presents the danger of
running lean (hot) @
WOT. |
|
Stock |
.037 |
.030 |
.063 |
.057
( largest
) |
The average
of jet sizes for all models.
Configured for complete combustion
of the fuel (emissions
standards). |
|
Street
Performance |
.048 |
.043
( largest
) |
.065 |
.052 |
Configured
for high-end performance and
low end fuel conservation.
Cruising mixture is set for less
than 2K RPM. |
|
Track
Performance |
.055 |
.027 |
.063 |
.045 |
Configured
for full range performance with an
emphasis on acceleration.
Cruising mixture set above 5K
rpm. |
|
Drag
Racing
performance |
.058
( largest
) |
.023
( smallest
) |
.067
( largest
) |
.043
( smallest
) |
Configured
for power under load at any RPM
over 5500. Very rich, and
virtually useless for track
or street. |
Fuel pressure should be
the same for all tuning configurations.
The Nikki that's tuned
for fuel mileage should have vacuum operated
secondaries.
Since economy
tuning needs quite a bit of driving time
between jet changes to record fuel
consumption, it's strongly suggested that plug
checking becomes a regular part of the
routine. Very light (or burnt) plugs is an
indication of running too lean. There is a
"tolerable" lean cruise mixture, but once
again, heat is the enemy, and even if the
engine isn't showing significant overheating
on the temperature guage, the porcelin on the
spark plugs could be in danger of
cracking.
And finally there is the
issue of timing. Admittedly, this is a weak
point for me, and as soon as I get some
reliable information on timing settings for
this type of tuning, I will surely add
it.
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