User guide

ThunderTech Products - 6655-A Amberton Drive - Elkridge, MD - 21075 - PH: [phone] - Fax: [phone]
READ INSTRUCTIONS FIRST!
OFF IDLE RESPONSE &
LOW TO MID-RANGE POWER
MID-RANGE TUNING
MID-RANGE AND TOP END
Jetting instructions continued on
the back of this page!
WE STRONGLY RECOMMEND THIS!
AIR FILTER
ACCELERATOR PUMP
INTERMEDIATE (LOW SPEED) JET
IDLE MIXTURE
THE AIR BLEED
MAIN JET
 This is the rst issue to
talk about because when making
changes here, it can change jetting
requirements.  The foam lter restricts
airow.Wehavefoundthebestalternative
isahighowK&Nlter.Itwillgiveyou
theperformanceyoudemandwhiledoing
abetterjoboflteringincomingairthan
afoamltercan.Westocktheseforall
S&Sapplicationsandalsomanufacture
alternativesystems.
 We recommend turning off
the accelerator pump when tuning the
intermediatecircuit.Itdoesn’tsupplyfuel
atsteadyspeedsandcanmaskproblems
ofaleancondition.Thisisevidentwith
plug readings that look good or even
rich and the next week you may have
twoburntpistons.Todisablethepump
whentuningahighperformanceengine,
turntheadjustingscrewclockwiseuntilit
contactsthepumparm.CAUTION: DO
NOT OVERTIGHTEN.  When tuning is
completeyoucanincreasepumptravel
toaidcoldstarts.Forbestresults,keep
thevolumelowonthiscircuit.Clearance
should be .020” to .030” @ adjustment
screw
 Thisisthenextstepafterincreasing
theintermediatejet.Disregardthefactory
settingonthiscircuit.Whenyoudrastically
increasetheintermediatejet,thismixturewill
berich.Insomecases,wendthecorrect
settingmaybeonly1/2turnoutfromtheseat.
NOTE:  Never richen this circuit to
compensate for lean conditions on the
intermediatecircuit.
rpmbeforefuelisdrawnfromtheMain
Jet,inordertocorrectarichfueloverlap
fromtheLowSpeedtoMain Jet circuit
transition.
 Now you can tune the Main
Jet in at a higher rpm level, when the
engine will want (and need) more fuel.
Thiscircuitcanalsohelpyoumanipulate
problems you may be experiencing
with certain hydraulic lifter camshafts,
exhaustsystemsandothercomponents.
These components might not allow the
enginetocarburetverywellinthemiddle
of the scale.The air bleed allows you
toremovesomeofthefuelvolumewhen
therequirementislow.Othercircuitsare
used to compensate for any demand.
Keepagoodselectionoftheseonhand
totuneforbestpower
 Nowthatyouhaveahandleon
theairbleedandintermediatecircuits,you
canusethemainjettoincreasethepower
in the mid-range and top-end.  When
you’re changing jets, keep in mind the
relationshipoftheairbleedtothemainjet.
Chances are that if you had good
poweratpeakrpmbeforeyouinstalled
the ThunderJet, you will probably
drop two sizes on the main jet after
installation.
Checkchartforstartingpoint.
Whenengineefciencyhasbeenincreased
via improved airow, compression, larger
displacement,etc.,thevolumeoffuelinthis
circuitmustberaised.Youincreasefuelto
increasepowerbutalsotoprevent engine
damage.  With a wide variety of engine
sizes, components and exhaust systems,
wecanonlyofferabroadrecommendation
of two sizes larger than stock setting,
some engines will require substantially
more.Callusforspecialjetsifyouneed
them.  This is truly a hidden treasure.
TUNE IT CORRECTLY!
 The Air Bleed is an air passage
connected to the Main Jet emulsion tube
thatallows air to mixwithfuelbefore it is
pulled into thecarb throat.You maynd
nowthatyou’veincreasedtheLowSpeed
jetsize,theenginerespondsbetteroffidle,
butnowhasastutterorhesitation(atspot)
astherpmrisestoalevelthatrecognizes
thecarb’sMainJet.Withthestocksized
(.042) Air Bleed, fuel starts being pulled
throughtheMainJetatarelativelylowrpm,
causingthis rich condition. Byincreasing
theAirBleedsize,youareineffectraising
therpmlevelneededtodrawmorefuelfrom
theMainJet.Simply,itallowsforincreased
THE AIR BLEED CONT’D
 After years of development on
S&S carburetors, we have noticed that
this circuit is the most misunderstood
in the overall picture of the fuel curve.
TOP END
THUNDERJET
 This circuit is doing a lot of
demand work.  Because of its built in
air bleed system, it becomes active at
approximately 4000-4200 rpms, while
the engine is under a controlled load.
UseThunderJet to tune(with the main
jet)formaximumpowerincreasesathigh
rpm.Ifyouaretuningonadyno,make
smalljetchangestoseethedifference
it makes. You will be surprised at the
powerincreases.
S&S G/D In S t a l l a t I o n a n D
tu n I n G In S t r u c t I o n S
These products are legal for sale in the State of California only for
racing vehicles which may never be used upon a highway.