S&S Cycle TWO THROAT Carburetor (Serial E1190 & Higher) User Manual

Page 6

Intermediate System

Up to 3000 RPM or 55-60 MPH

For normal riding conditions, the intermediate
range is used the most. Therefore, close
attention must be paid to jetting the mid-range
to achieve optimum performance and gas
mileage. Once the engine is warmed up and
the idle mixture and engine RPM screws set,
the bike must be road tested. The intermediate
range is used from right off idle up to
approximately 3000-3500 RPM or 50 to 60
MPH depending on gearing. Throttling
characteristics can be checked by slowly
opening the throttle (so as to not energize the
accelerator pump) after maintaining a steady
speed. This can be done at several RPM levels
or speeds of 30, 40, and 50 MPH. If popping or
spitting occurs in the air cleaner, this is a lean
condition and should be corrected. Another
indication of a lean intermediate system can be
noticed by feeling a "flat" or "laboring"
condition while cruising at 55 to 60 MPH, right
at the top of the intermediate range.

NOTE - As mentioned earlier, it is extremely critical that
the idle mixture screw and throttle stop screw be adjusted
with a hot motor. The idle will effect the intermediate
system and if it is not adjusted properly, one will not get a
true reading as to the performance of the intermediate.

If the intermediate system is too rich, it may
show up by popping in the pipes, a "lope" or
miss at lower RPMs, or a miss or stutter at
transition, about 3000 to 3500 RPMs, especially
in low gear under reduced load conditions.

To lean the intermediate, install a smaller set of
intermediate jets, Part #11-7300. One may also
make subtle changes by bleeding in more air by
installing larger air bleeds, Part #11-7320.

To richen the intermediate system, install a
larger pair of intermediate jets and/or smaller
air bleeds

NOTE - A properly jetted intermediate system will act lean
(cough or spit) when the engine is cold and will require riding
a few miles to warm the engine to operating temperature.

Higher altitude or hot, dry weather may require
a leaner mixture (smaller intermediate jets
and/or bigger air bleeds) while lower altitude,
cold weather, or a warm and humid climate
may require a richer mixture (larger
intermediate jets and/or smaller air bleeds) to
dial the system in properly.

We have run a:

900cc Harley-Davidson

Sportster

model

with the .029-.046 intermediate combination.

1000cc Sportster

model with .030-.046.

Stock 74" panhead with .029-.046.

80" shovelhead with .030-.046.

98" shovelhead with the .033-.046
combination.

Main Jet

From 3000 RPM or 55-60 MPH and up:

Main jetting is best determined by testing at the
drag strip. Jetting should always be done at
operating temperature. After a run is made, the
engine RPM and final speed should be noted.
A second run should be made with a .004
larger, richer, jet installed. Again, RPM and
final speed is noted. This procedure should be
continued until the miles per hour falls off. The
main jet should then be made smaller (leaner)
to gain the best maximum RPM and MPH.
When making these runs, do not strive for ETs,
but for consistent miles per hour. We have
found that maximum miles per hour and RPM
have been the best indicators of proper jetting.

If the engine is buttoned off after each run, the
spark plugs may be inspected for richness or
leanness. Plug color though is not always a
good indication of carb jetting on quarter mile
tests. We have found that different brands of
gasoline, gasoline additives, engine heat (due
to ignition timing), and type of plugs and heat
range used alter readings drastically. New
plugs usually require the time involved in a
road test to properly develop the plug color. It
is best to use a proven combination and to
consult the spark plug manufacturer for more
specific information if one desires to become
proficient at plug reading. Champion Racing
Division has a very informative booklet. For
details, write:

Champion Spark Plug Company

P.O. Box 910

Toledo, Ohio 43601