Zipper's Performance E/B Carbs - Manual (Page 4)

Tapping bowl vent for fitting.
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GENERAL INSTRUCTIONS
EXTERNAL FLOAT BOWL VENT
ADJUSTABLE AIR BLEED
CIRCUIT
If you do not have the facilities to
properly install this fuel module,
professional installation is available
from Zipper’s. High volume shops
may want to invest in our ThunderJet
installation fixture (shown in the
photos p/n 713-910) which securely
holds the carb body and float bowl at
the correct positions for machining.
Use with a mill when installing
ThunderJets in all S&S model E/G/
B/D carbs. Read all instructions fully
and carefully before proceeding any
further.
Loosen drain plug and remove float
bowl and manifold. Install two (2)
studs in carb manifold bosses; use
these to center carb in milling machine
vise. Be careful not to over tighten
carb in vise. The first two steps are
recommended to further enhance
your carb’s performance along with the
installation of your ThunderJet.
1. Pressure in the float bowl is
stabilized with the addition of this
external bowl vent. Locate the new
vent hole in the rear of the carb wall
.438” above bowl gasket surface
and 1.906” from the manifold flange
of the carb. Open hole with a small
center drill then plunge a 5/16” end
mill to a depth of .562” below the
raised surface. Use a ½” countersink
to chamfer the raised surface to help
start the tapping process. Chamfer
only slightly not touching the lower
level surface. Tap with 1/8” NPT tap.
Install 1/8” NPT street elbow and
1/8” NPT x 3/8” hose nipple using
a suitable thread sealer. The hose
nipple should be positioned pointing
up.
Air bleed passage drilled & tapped
for jet.
Fuel tube hole drilled/tapped, area
relieved for ThunderJet
THUNDERJET INSTALLATION
2. All “B” model carbs are
manufactured with a fixed size air
bleed passage. This modification will
allow the tuner to adjust the main jet
air bleed size for more control over the
main jet circuit signal timing and fuel
volume. Locate the fixed air bleed hole
and bore with 1/4” drill until you reach
the cross drill in carb (DO NOT GO
PAST CROSS DRILL!!). Spot face
the area with 1/2” end mill for mating
surface of jet. Use 5/16-24 starter tap
in hole and remove to use a 5/16”
bottom tap to finish job. Original air
bleed size is .042”; suggested range is
.054-.072”. Use S&S main jets for this
application.
NOTE: On “B” applications using
only (1) ThunderJet, the ThunderJet
mounts on the side of the carb facing
the rear of the bike (9:00 position). If
using (2) ThunderJets follow all in-
structions below and mount one each
in the 9:00 and 3:00 positions.
9:00 POSITION
3. Drill and tap hole .750” from the
end of the carb throat, offset slightly
above the throttle butterfly shaft. Use
a #3 drill and tap 1/4-28 thread. You
will be drilling through the middle of the
original float bowl vent passage; this
is OK, it will not affect performance or
operation of the carb.
4. You then need to relieve the area
around the hole you just threaded for
air bleed spacer clearance. This is
best accomplished on a vertical mill
with a 3/4” end mill. With the cutter
starting near the bowl area, mill toward
the top of the carb, removing material
at least ¼” above the centerline of the
fuel tube hole. Use care not to break
into the enrichener air passage located
above the hole. Leave .170-.185” of
carb wall for the short threaded portion
of the fuel delivery tube.
Double-nut and tighten fuel tube
in place
D
O nOT OveRTighTen bODy
OR fuel Tube bReAkAge
will ResulT
!
ThunderJet body (nipple down),
bowl cent & air bleed jet in place.
5. Install the fuel delivery tube from
the inside of the carburetor throat out.
Double nut the delivery tube using (2)
¼”-28 jam nuts and carefully lock into
carb throat (DO NOT OVERTIGHTEN).
Remove jam nuts (not needed after
this step).
6. Install air correction spacer, o-ring,
and ThunderJet with fuel nipple facing
down towards float bowl. Trim small
opening side of air correction spacer,
if needed, to achieve a hand tight
location 1/6 of a turn from permanent
location and finish tightening with
wrench. (.006” trim = 1/6 turn).
3:00 POSITION
(Part 2 of twin T-Jet installation)
7. Drill and tap hole .950” from the end
of the carb throat (#3 drill and 1/4-28
tap), offset slightly above the throttle
butterfly shaft.
8. You then need to relieve the area
around the hole you just threaded for
air bleed spacer clearance. This is
best accomplished on a vertical mill
with a 3/4” end mill, on center of your
threaded hole. Be certain to leave .170-
.185” of carb wall for the short threaded
portion of the fuel delivery tube. (On a
“B” carb with twin ThunderJets, you will
be cutting through the float bowl vent
passage. This passage must then be
plugged, as its location will subject the
passage to positive air pressure at
speed, resulting in fluctuating pressure
in the float bowl, adversely affecting
jetting. Drill the passage past the
ThunderJet mounting area and tap it
5/16”, 3/8” deep and plug it with a set
screw. The external vent described in
step 1 must be performed to replace
this original vent.)
Hole A (standard 9:00 position),
B (3:00 position, if twin T-Jets are
used)
13. ReAD Tuning
insTRuCTiOns
FOAT BOWL
3 o’clock position, fuel tube hole
drilled/tapped, area relieved for
ThunderJet, fuel tube installed.
Circled area shows where vent
passage should be plugged
9. Follow steps 5, 6 & 7 from the
9:00 segment.
10. Clamp bowl to mill table at 35
degree angle. See photo for bowl nipple
location(s). At the bottom of float bowl,
beside drain, drill a #3 hole and tap
¼”-28. Spot face the area around the
hole to give a flat surface for the o-ring
to seal against and reduce thickness
enough to allow the nut to attach on
the inside of the bowl. Install fuel
nipple and o-ring then secure inside
bowl with nut provided (no washer).
Stake threads with a punch to lock
nut in place (make sure this device
does not interfere with float action or
movement). Repeat for multiple bowl
nipple locations.
12. Clean all carb parts; reassemble
and install fuel line with clamps
provided (trim fuel line if needed).
Install on engine. Install fuel line,
turn fuel valve on and check for leaks
before starting engine!!
ThunderTech Products - 6655-A Amberton Drive - Elkridge, MD - 21075 - PH: (410)579-2929 - Fax: (410)579-2835