Instruction Manual

Tapping bowl vent for tting.
Fo R s&s ‘b’
ca R b u R e t o R s
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 xture (shown in the
photos p/n 713-910) which securely
holdsthecarbbodyandoat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oat
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rsttwostepsare
recommended to further enhance
yourcarb’sperformancealongwiththe
installationofyourThunderJet.
  1. Pressure in the oat 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 ange
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 xed size air
bleedpassage. This modication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xed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 nish 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butteryshaft.Use
a#3 drillandtap1/4-28thread. You
willbedrillingthroughthemiddleofthe
original oat 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
DO n O T O v e R T i g h T e n b O D y
O R f u e l T u b e b R e A k A g e
w i l l R e s u l T !
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 oat 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 nish 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
buttery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oatbowlvent
passage.Thispassagemustthenbe
plugged,asitslocationwillsubjectthe
passage to positive air pressure at
speed,resultinginuctuatingpressure
in the oat 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oatbowl,
beside drain, drill a #3 hole and tap
¼”-28.Spotfacetheareaaroundthe
holetogiveaat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 oat 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: [phone] - Fax: [phone]