User guide
Fo R s&s ‘d’
ca R b u R e t o R s
GENERAL INSTRUCTIONS
ThunderTech Products - 6655-A Amberton Drive - Elkridge, MD - 21075 - PH: (410)579-2929 - Fax: (410)579-2835
A.
Tapping bowl vent for tting
EXTERNAL FLOAT BOWL VENT
ADJUSTABLE AIR BLEED
CIRCUIT
Ifyoudonothavethefacilitiestoproperly
install this fuel module, professional
installation is available from Zipper’s.
Highvolumeshopsmaywanttoinvestin
ourThunderJetinstallationxture(shown
inthephotosp/n713-910)whichsecurely
holdsthecarbbodyandoatbowlatthe
correctpositionsformachining.Usewitha
millwheninstallingThunderJetsinallS&S
modelE/G/B/Dcarbs.Readallinstructions
fullyand carefullybefore proceedingany
further.
Loosendrainplugandremoveoatbowl
andmanifold.Installtwo(2)studsincarb
manifold bosses; use these to center
carb in milling machine vise. Be careful
nottoovertightencarbinvise.Therst
two steps are recommended to further
enhance your carb’s performance along
withtheinstallationofyourThunderJet.
1.Pressureintheoatbowlisstabilized
withtheadditionofthisexternalbowlvent.
Locatethenewventholeintherearofthe
carbwall.438”abovebowlgasketsurface
and1.906”fromthemanifoldangeofthe
carb.Openholewithasmallcenterdrill
thenplungea5/16”endmilltoadepthof
.562”belowtheraisedsurface.Usea½”
countersinktochamfertheraisedsurface
tohelpstartthetappingprocess.Chamfer
only slightly not touching the lower level
surface. Tap with 1/8” NPT tap. Install
1/8”NPTstreetelbowand1/8”NPTx3/8”
hosenippleusingasuitablethreadsealer.
The hose nipple should be positioned
pointingup.
Air bleed passage drilled & tapped
for jet.
Fuel tube hole drilled/tapped, area
relieved for ThunderJet
THUNDERJET INSTALLATION
2. Earlier versions of “D” carbs are
manufactured with a xed size air bleed
passage (current “D” models are now
machined for adjustable air bleed jets).
This modication will allow the tuner to
adjustthemainjetairbleedsizeformore
control over the main jet circuit signal
NOTE: On“D”applicationsusingonly(1)
ThunderJet,theThunderJetmountsonthe
sideofthecarbfacingtherearofthebike
(9:00position).Ifusing(2)ThunderJetsfol-
low all instructions below and mount one
eachinthe9:00and3:00positions.
timing and fuel volume. Locate the xed
air bleed hole and bore with ¼” drill until
youreachthecrossdrillincarb(DO NOT
GO PAST CROSS DRILL!!)
.Spotfacethe
area with 1/2” end mill for mating surface
ofjet. Use 5/16-24 starter tapinhole and
removetousea5/16”bottomtaptonish
job.Originalairbleedsizeis.042”andthe
suggested range is .054-.072”. Use S&S
mainjetsforthis.
9:00 POSITION
3. Drillandtaphole.750”fromtheend
ofthecarbthroat,offsetslightlyabovethe
throttlebutteryshaft.Usealetter‘i’(.272”)
drill and tap 5/16”-24 thread. You will be
drilling through the middle of the original
oatbowlventpassage;thisisOK,itwillnot
affectperformanceoroperationofthecarb.
4. You then need to relieve the area
around the hole you just threaded for
air bleed spacer clearance. This is best
accomplishedonaverticalmill witha3/4”
end mill. With the cutter starting near the
bowlarea,mill towardthetop ofthecarb,
removing material at least ¼” above the
centerline of the fuel tube hole. Use care
nottobreakintotheenrichenerairpassage
locatedabovethehole.Leave.170-.185”of
carbwallfor the short threaded portion of
thefueldeliverytube.
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.Installthefueldeliverytubefromthe
insideofthecarburetorthroatout.Double
nutthedeliverytubeusing(2)¼”-28jam
nuts and carefully lock into carb throat
(DONOTOVERTIGHTEN).Removejam
nuts(notneededafterthisstep).
6.Installaircorrectionspacer,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
ofthecarbthroat,offsetslightlyabovethe
throttle buttery shaft (letter ‘i’ (.272”) drill
and5/16”-24tap).
8. Youthenneedtorelievetheareaaround
theholeyoujustthreadedforairbleedspacer
clearance.Thisisbestaccomplishedona
verticalmillwith a3/4”end mill,oncenter
ofyourthreadedhole.Becertaintoleave
.170-.185”ofcarbwallfortheshortthreaded
portionofthefueldeliverytube. (Some D
carbs are equipped with dual oat bowl vent
passages (forward and rear of carb throat);
you will be cutting through the forward vent
passage if equipped. 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 (9:00 position), B (3:00),
C (12:00)
13. ReaD Tuning
insTRuCTions
FOAT BOWL
PRO-STOCK OPTION
(12 O’Clock Position)
Spot faced, drilled/tapped for 3rd
T-Jet (Pro-Stock option)
fuel tube hole drilled/tapped,
area relieved for T-Jet, fuel tube
installed. Circle shows where vent
passage should be plugged
9. Follow steps 5, 6 & 7 from the 9:00
segment.
IfathirdThunderJetisdesired,drill,tap
(letter‘i’(.272”) drilland5/16”-24 tap)and
spotfaceTOPcenterofcarb1.200”fromair
cleanerbackingplatesurface,leaving.170-
.185”wallthicknessfortheshort threaded
portion of the fuel delivery tube. Follow
steps5,6&7fromthe9:00segment.Point
hose nipple towards rear of the bike and
slightlyinward.
10. Clampbowltomilltableat35degree
angle.Seephotoforbowlnipplelocation(s).
At the bottom of oat bowl, beside drain,
drilla#3holeandtap¼”-28.Spotfacethe
areaaroundtheholetogiveaatsurface
for the o-ring to seal against and reduce
thicknessenoughtoallowthenuttoattach
ontheinsideofthebowl.Installfuelnipple
ando-ringthensecureinsidebowlwithnut
provided(nowasher).Stakethreadswitha
punchtolocknutinplace(makesurethis
devicedoesnotinterferewithoatactionor
movement).Repeatformultiplebowlnipple
locations.
12. Clean all carb parts; reassemble
and install fuel line with clamps provided
(trimfuellineifneeded).Installonengine.
Installfuelline,turnfuelvalveonandcheck
forleaksbeforestartingengine!!