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A very inclusive guide to Thermoquad carburators, written by Gary Lewallen  (aka. Vaanth).  A must read for anyone running one.


                      A Carter Thermo-Quad Guide

Author:  Gary Lewallen  (aka. Vaanth)
Date:    24 February 1998
Copyright 1998  Gary Lewallen

= Introduction
= History and Description
  - General
  - Identification
= Subsystems
= Port Diagram
= Choices and Adaptations
= Numeric Listing
  - Thermo-Quad
  - Rochester Quadrajet
= Modification of Subsystems
= References
= Acknowledgements


The Carter Thermo-Quad is a four-barrel carburetor with a spreadbore
throttle bore configuration.  It was designed as an emissions capable
carburetor that retained or surpassed secondary throttle performance of
earlier Carter carburetors, while delivering superior primary fuel
economy.  The Thermo-Quad consists of three main sub-assemblies,
an aluminum fuel bowl cover, a phenolic resin main body, and an
aluminum throttle base assembly.  The Thermo-Quad derives its name from
the phenolic main body.  Due to the material of the body, the carburetor
bowl can stay 20 degrees cooler than an all metal carburetor in the same
environment.  The Thermo-Quad was used by Chrysler Corporation in cars
and trucks 1971-1984.  Aftermarket versions were also produced by Carter.

This guide is intended to provide information for identifying Thermo-Quad
carburetors and related items.  It provides a basic history and basic
descriptions of the carburetor and its subsystems.  It is not intended
as a full theory of operation manual nor a repair manual.  Service
documentation should be consulted for repair procedures and service
details.  The factory service manuals provide good service procedures
and theory for specific models.  Other sources may be consulted for
general repair and modification procedures as well as theory of operation.
See the list of references for sources.

This guide is written with carburetor 'swapping' in mind.  Thus, certain
items are discussed with modification consideration (ie. emission subsystem
disablement) with the intent for adapting a non-original carburetor and/or
enhancing performance.  The modification and adaptation of the carburetors
may present legal issues, so consider the interest of any appropriate

History and Description...

- - - -
The Thermo-Quad (TQ) was initially released for competition in 1969.  Chrysler
introduced the TQ on the 1971 340.  The first series of TQs including the
71 340 version and the Competition Series TQs were air metered units
unlike like the 72 and later TQs which were solid (liquid) fuel metered.
The Competition Series (CS) were available in 850 cfm and 1000 cfm ratings.
CS units use a manual choke and have a minimal amount of external attachments
compared to OEM production units. The CS was discontinued in the mid-70s.
Carter released the 9000 series in the latter 70s as replacement carburetors
for Chrysler and GM Quadrajet applications.  The 9000 series was very
similar to the production Chrysler Thermo-Quads.

In 1972, the OEM Chrysler TQs changed to the solid fuel metering type.  The
TQ coverage was expanded to include the 400 engine.  By 1973, all Chrysler
4-bbl applications were TQs (except some 413 truck models which continued to
use a Holley carburetor).  As the years progressed, the TQ evolved to meet the
continually tightening emissions requirements.  The changes were numerous.
Many features were added or modified externally and internally. The late
70s contained many variations for the various geographic regions, the
various features included/excluded, and the range of applications and engines
produced.  Into the 80s, the TQ became more complex, but year to year major
variation lessened somewhat.  In 1973, TQs received a port on the base for
canister purge and a port on the main body to provide a venturi vacuum signal
for EGR applications.  1975 saw the introduction of the Idle Enrichment system,
Altitude Compensator on some models, and the  Throttle Position Solenoid for
the new catalytic converter equipped cars.

In 1976, Chrysler introduced Lean Burn ignition and the TQ was modified
to produce and run on a very lean air/fuel mixture.  An external idle stop
switch and throttle position tranducer were added.  In 1978, the TQ bowl
vent was modified with the addition of an electric Bowl Vent solenoid.  An
additional rear base port for the vent hose replaced the bowl vent port. The
fuel inlet moved to the rear center of the carburetor from the previous
rear side location.  Lean Burn became Electronic Spark Advance (ESA) in
1979.  The very lean mixture idea was abandoned, but the electronic control
of the ignition advance was retained.  Hidden mixture screws were a feature
starting with some 1980 model TQs.  1981 introduced a riveted cover for
the choke pull-off linkage to prevent tampering and the oxygen feedback
solenoid on some models.  Idle Enrichment and Altitude Compensator was not
used on feedback models.  82-84 did not change much more in a major way.
The canister purge was eliminated by 84 in some applications and a power brake
port was added to the rear base.

After 1984, Chrysler stopped using Thermo-Quads.  Instead, the Rochester
Quadrajet was used through 1989 on cars and until 1988 in  trucks when
Electronic Fuel Injection replaced them.  Carter continued to supply the
fuel pumps for the Quadrajet equipped vehicles.  Although Chrysler was the
primary manufacturer to use the TQ, International Harvester (IHC) used them
in the late 70s and Ford used them in 1974.

The Thermo-Quad was available with two primary throttle bore sizes, 1-3/8"
and 1-1/2".  Flow ratings (CFM) vary depending on the source, but
the TQs with the 1-3/8" bores are listed as 750-800 CFM and those with the
1-1/2" primary throttle bores are rated at 800-850 CFM.  All TQs have the
2-1/4" diameter secondary throttle plates. The primary bore size depended
on application.  In general, all 78 and later 318s and 360s and all 340s had
the smaller bore.  Earlier 360s varied depending on application, most 400s
and all 440s had the large bore.  The 9000 series have the small primary bore
and were rated by Carter at 800 cfm.  Later TQs (ie, Lean Burn and ESA
applications, feedback systems) are quoted with less flow ratings, but
this is due to the control of the carburetion system, not the inherent
flow capability of the basic carburetor.  The internal metering is set for
leaner running conditions for Lean Burn.  Either bore size can be tuned
to run well on most engine combinations.  The smaller bore offers a slight
increase throttle response but less overall flow. The different bore sizing,
ie. speadbore, is an aspect that can lead to increased fuel economy while
delivering similar wide open throttle (WOT) performance to an equivalent
standard bore configuration.  The adjustability of the TQ and the
spreadbore configuration allows the use of a large CFM carburetor on
a small displacement engine.

The TQ gets its name from the phenolic resin main body.  This is "sand-
wiched" between the aluminum bowl cover assembly and the lower throttle
flange assembly.  The plastic body keeps the fuel ~20 degrees cooler
than an all metal carb in the same enviroment, leading to less percolation
problems and increased performance due to a denser charge.  The TQ is a
metering rod based carburetor like other Carters (AFB, AVS, BBD).  The
primary jets are housed in the plastic body, the primary metering rods
are suspended from the cover mounted step-up piston assembly into the
jets (in the 71 TQ and the CS, the primary jets are also housed in the cover).
Engine vaccuum (related to load) controls the position of the metering
rod in the jet, metering the fuel flow.  The secondary jets are suspended
from the cover.  Secondary flow is controlled by variable venturi effect in the
secondary bores.  The TQ secondary throttle plates are controlled by direct
mechanical linkage, air flow is controlled by a secondary, spring tension
resisted, air valve.  The valve is further controlled and damped by the choke
pull-off diaphragm.

The OEM TQs have a divorced choke (73-up with electric assist in most
applications), the 9000 series have an integral electric choke, and the
CS were equipped with a manual choke.  All OEM TQs and later CS have
screw-in jets.  Early CS retained the jets via O-rings.

- - - - - - - -
To identify TQs, the model number is stamped on the lower left rear
bolt flange.  Earlier TQs also had a tag under one of the front bowl cover
screws, later ones  have a bar code sticker on the bowl cover with the
Carter model and/or a Chrysler part number.  International Harvester
TQs also have a tag under a front bowl cover screw.

Additional numbers will be found on the carburetor sections.  These
numbers are not used for TQ identification, but some can be used to relate
one casting to the other (note that parts with the same casting number
may be machined differently).  The upper bowl cover has the casting number
on the top, right of center rear: 6-XXXX (example: 6-2141, 6-2080, 6-2024).
The bowl has the casting number molded on the bottom of the right bowl
near the front, it is difficult to see with the throttle base on the carb:
0-XXXX (example: 0-2511A, 0-1823, 0-2709A).  The throttle base has the
casting number on the right upper side in a small recess: 1-XXXX (example:
1-2357, 1-2294, 1-2967.  More numbers will be found ink stamped, cast or
stamped in various areas.  Moreover, numbers are usually stamped below
the model number on the lower left rear bolt flange.  The model number
consists of four digits, usually followed by an 'S' (ie. 6318S).  The
model number is the primary and documented identifier.

The 71 OEM units can be identified externally by the mixture screws which
protrude at an angle from the base, in the same plane as the base, later
units protrude perpendicular to the base plane, but angle upwards from it.
Note: some 1980 and later units have hidden mixture screws.  The
Competition Series have raised pads on the upper bowl cover for a label.
Also, the CS have minimal external attachments, such as the lack of a PCV
port.  The mixture screws are similar to the 71 OEM TQs.

The fuel inlet on the CS and the 78-84 OEM units was located in the rear
center and the 71-77 OEM and 9000 series have the fuel inlet on the right
rear side.  The aftermarket 9000 series were available in 4 models:
9801, 9811, 9800, 9810.  The 9801, 9811 have Chrysler linkage (9801/9811
is EGR capable).  Note:  later OEM TQs model number started with a 9 as well,
but are not to be confused with the aftermarket 9000 series.

TQs with 1-3/8" primary throttle bore will have '2-315' stamped on the
throttle plates.  1-1/2" units will have '2-314' stamped on the plates.
All secondary plates are stamped with '2-312'.

This section briefly describes the primary Thermo-Quad subsystems that
are readily accessible and the various attachments for emissions.  For
detailed theory of operation of the subsystems or general operating
functions such as the low and high speed metering circuits, refer to
the references listed in the References section, specifically the
Carter Thermo-Quad service manual.  See the Service Parts Information
section for details on parts and part numbers.

- Jets:  jets are contained in the primaarry and secondary circuits, one
for each barrel.  Early CS units had press-in jets retained by o-rings.  CS
and 71 TQs have the primary jets in the upper bowl cover.  All other
TQs have screw-in primary jets in the main body.  All TQs have the
secondary jets mounted in the upper bowl cover.  All jets have a part number
prefix of 120-.  72 and later TQs usually have the part suffix stamped
on the jet, primaries: 4XXX, secondaries: 5XXX (or 120-5XXX).  The XXX
denotes the size, example:  4098 = 0.098", 5137 = 0.137".  CS and 71 TQs
have part number suffixes of 3XX or 3XXX.

- Metering rods and step-up:  metering rroods meter the fuel through the
primary jets.  They are essentially controlled by engine vaccuum and a
mechanical link, step-up cam/lever, connected to the primary throttle shaft.
Many variations of metering rods were available through the years.  The
depth of pre-76 models could be adjusted to tune, ( primarily ), cruising
condition flow via a screw adjustment.  Some later models retained this
feature, but starting in 1980 may have the adjustment locked via a collar.
Metering rods have three steps for metering, economy, midrange, power.
They are usually stamped with a part number, 75-XXXX or XXXX where the
XXXX defines the step sizes.  The CS and 71 TQs have numbers 16-XXX.

- Floats:  TQs are a single fed, dual innllet, dual bowl carburetor.  One
bowl feeds each carb half, ie. one primary and one secondary.  The dual
bowl arrangement is contained in the phenolic main body.  Dual floats
and dual inlet valves are employed.  Early TQs used brass floats. 
Later models (73-74 and later) use nitrophyl floats.  All OEM TQs are
equipped with needle & seat number 25-1086 (0.0935" orifice).

- Accelerator pump:  the accelerator pummpp is located on the left front and
feeds from the left fuel bowl.  The pump is activated by the left side
throttle bracket.  There is some stroke adjustability at the upper lever.
The fuel is transfered via a plastic tube internally to the squirter
which resides above the primary venturi.  Later models have two adjusment
holes instead of three, and perform a two stage pump that add additional
fuel as the secondaries open.  Three accelerator pump clusters (squirters)
were available.

- Secondary air valve:  TQ secondary thrroottle plates are mechanically
linked to the primary on the left side.  As the plates begin to open,
the secondary air valve senses the opening and begins to open to provide
air flow which starts fuel flow from the secondary jets.  The initial
opening and rate is determined by a counteracting tension spring inside
the cover.  The opening is additionally regulated and dampened by the
choke pull-off assembly.  The air valve is contoured and the movement
provides a variable venturi effect.  A secondary fixed baffle is mounted
below the air valve.  Total air valve movement is limited by a protruding
tab.  The counteracting spring tension is adjustable via a slot/lock screw
on the left side to tune the rate.  Carter designed a special tool to
facilitate this adjustment.  Some of the CS TQs used an adjustment and
lock screw arangement similar to the AVS.

- Choke:  OEM TQs use a divorced, manifoolld mounted choke.  Exhaust crossover
heat operates the thermostatic spring contained in the choke well.  Most
73-84 TQs were electrically assist heated.  The electric control is via
a small module mounted to the intake or right head.  This unit times the
assist based on temperature and time and receives power from the ignition
run circuit.  9000 series have an integral choke assembly identified by
the black, circular plastic thermostat housing.  This unit is electrically
controlled.  CS units have a manual choke.  Choke action is accomplished
via the choke plate in the top of the primary side.

- Mixture screws:  screws used through 119976 had a 20 degree taper at the
seat.  In 1977, this was changed to 12 degrees to reduce adjustment
sensitivity.  Some ~77-79 TQs also contained internal restrictors to
limit adjustment.  Plastic caps with tabs to limit adjustment were also
installed on several models.  Many 1980 and later TQs had the base
redesigned to enclose the mixture screws so they could be 'capped' via
plugs after factory setting.

- Choke pull-off:  All TQ models.  This  pperforms the vacuum kick
pull-off function for the choke at initial cold engine start.  It is
also used to regulate and dampen secondary air valve opening.  Mounted
on the right rear base under a mounting bolt and screw.  Connects to
the rear vacuum port, right, color code gold.  The CS has the diaphragm
for secondary air valve control only.

- Hot Idle Compensator:  Some models aree  equipped with a compensator to
allow exta air into the mixture during high heat conditions.  If equipped,
it is located on the bowl cover over the secondary air valve.  High
temperatures can create an over-rich idle condition, and this compensates
for it, by allow extra air flow when it opens. 

- Idle Stop Solenoid (ISS):  71-76.  Useedd to set the idle higher than the
basic curb idle screw for emissions reduction and to allow further
closure of the throttle blades at engine shutdown to prevent 'deiseling'
or 'run-on'.  Mounts on a bracket retained by base mounting bolt and
screw on the right side for 72-76.  71 mounted to the left side of the
intake under the carb linkage.

- Exhaust Gas Recirculation (EGR) port:    73-84, not used in some 76~81.
Some located on the main phenolic body as a tap into the venturi for vacuum
signal.  Venturi port is connected to a vacuum amplifier if used.  Some
models use a ported signal via a base port on the right front.  Base
ports color coded black.  Venturi ports are brass.

- Evaporative Control System (ECS) port::  73-84.  Used to purge the ECS
charcoal canister of collected gas fumes from the bowl vent and fuel
tank vent.  Color coded red.

- Idle Enrichment (IE) system:  75-81.  TThis is a driveability enhancement.
It supplements th choke function by allowing an even richer mixture during
the warm up period to improve driveability.  This will appear as a small
attachment on the front bowl cover that has a vacuum port that connects
to a coolant temperature sensor (CCIE), then to manifold vacuum with bleed.
It will also be plumbed into the EGR delay timing system.

- Altitude Compensator or Alcomp (Alc):    75-81.  This is another driveability
enhancement.  It appeared on most California and Federal high altitude
cars.  It appears as a small cylinder attaced to the front of the Idle
Enrichment system at the front of the bowl cover.  A small bellows inside
reacts to altitude changes and alters the air flow in the high speed
metering circuit.  This improves driveability and reduces emissions by
maintaining a correct fuel/air mixture.  Note:  later vehicles may be
equipped with a remote Alcomp sensor (fenderwell) to signal the feedback
solenoid controller to compensate.

- Bowl Vent (BV) solenoid:  78-84.  In aann effort to completely capture all
fuel bowl evaporative emissions, the standard bowl vent was redesigned
with a two way valve and holding solenoid at the rear of the carburetor.
When the engine starts, manifold vacuum pulls the valve rubber 'puck'
down, opening the bowl to the canister port.  The solenoid is connected
to the ignition run circuit and holds the valve open during low vaccuum
periods while running.  When the engine is shutdown, the valve releases and
reseals the float bowl.  Connects to rear base port, color code gold.

- Ground Switch:  76-84.  This appeared  wwith Lean Burn (LB).  It signals the
computer that the throttle plates are at idle position.  Later models
with solenoid idle stop combined the functions.  It is located on the
bracket on the right front.  A throttle shaft attachment contacts it.

- Throttle Position Transducer (TPT):  7766-81.  This appeared with Lean Burn.
It signals the position and movement rate of the throttle to the computer.
It is attached via the same bracket as the Ground Switch.

- Solenoid Idle Stop (SIS):  81-84.  Useedd to set the idle higher than the
basic curb idle when additional heavy accessory load (ie. rear window
defogger, air conditioning) is placed on the engine.  Mounts on a
bracket on the right front.

- Dashpot:  Some models, primarily truckkss, may have a dashpot to slow
throttle closing rate to reduce stalling.  Mounted on a bracket on the
left front.

- Vacuum Pull-Off Choke:  A few models mmaay have an additional pull-off
mounted on the left rear.  This connects to manifold vacuum via a control
switch in the vacuum plumbing.  It prevents choke operation after
engine warmup.

- Throttle Position Solenoid (TPS):  75--llater, some models.  Mounts in the
same place as the idle solenoids and is used to delay full throttle closure
at deceleration to prevent a momentary rich condition thus protecting
the catalytic converter(s).

- Vacuum Throttle Positioner (VTP):  75--llater, some models.  Mounts in the
same place and performs the same funcion as the Throttle Position Solenoid.
Also serves as a speed sensor.

- Pulse Solenoid, Oxygen Feedback Controoll (O2):  81-84.  Mounts on the
front of the bowl cover (where the IE module mounted earlier).  This
solenoid is used to control the air/fuel mixture via varying duty cycle
pulsing from the control computer based on feedback from exhaust, engine,
and ambient sensors.

- Fuel bowl inserts:  some later models  hhad an insert in the fuel bowls to
reduce the bowl fuel volume.

- Choke pull-off cover:  many 81-84 modeells have a cover to prevent field
adjustment of the pull-off.

Port Diagram

This section contains a diagram and notes to identify the various hose
port connections on the Thermo-Quad.  Different port configurations were
used throughout the years.  The diagram is a representation of the
throttle base, top view.  It is drawn with all possible ports.  The
label notes identify the ports and their general usage.  Some ports are
contained in the bowl or bowl cover.  These are also identified.  The ports
are labeled by (x)...descriptions follow the diagram.


                                  ___    _       
                            (B)  |  |  | |
        ||  ||  |  |  | |    ||  //(F)
||  ||  |  |  | |    ||  //
| O (A)   (C)* (D) (E)  O |    /|
| |    / |(G)
| |  /  |
|   -----          ----- |---  /
| /    \        /    \ |    /
| |      |      |      | |---
      =| |=O===O=|      |=O===O=| |=
| |      |      |      | |
| \    /        \    / |
|   -----          ----- |
|      -----------    -----------      |
|    /          \  /          \ |
|    |            | |            |    |
|    |            | |            |    |
      =|    |===O=====O===| |===O=====O===|    |
|    |            | |            |    |
|    |            | |            |    |
|    \          /  \          / |
|      -----------    ----------- |
| |
| |
| |
| O (H) (I)  (J)  (K)    (L)       O |
---||--|---|-||--|---|---||------------  -------
                    ||  |  | ||  |  |  ||              \    /
                    ||  |  | ||  |  |  ||                -----
                        /  /    |  |                      //
                      /  /      |  |                      (M)
                      /  /      |  |
                      ---        |  |


- (A) Distributor Vaccuum Advance (blackk,, 71-75, some 76-84), 5/32".
- (B) Idle Enrichment (IE) (gold, 75-81  ssome models), 5/32".
- (C) PCV (gold, 71-84), 11/32". * Note::  angled on 80-84 models.
- (D) Canister Purge (ECS) (red, 73-82),,  1/4".
- (E) EGR (gold) or Air Pump (blue), 5/3322".
- (F) EGR venturi port (brass), 1/8", {lloocated on phenolic float bowl}.
- (G) Bowl Vent (gold, 71-77), 11/32", ((llocated on the upper bowl cover}.
- (H) Air Cleaner Heated Air Temp Sensorr  (black, 78-84), 5/32".
- (I) Power Brake Tube (gold, 81-84), 111//32".
- (J) Air Cleaner Heated Air Temp Sensorr  (black 71-77), 5/32",
      Bowl Vent Solenoid Vacuum Tube (gold 78-84), 5/32".
- (K) Canister Bowl Vent Tube (gold, 78--884), 11/32".
- (L) Choke Pull-off (gold, 71-84), 5/322"".
- (M) Choke Pull-off Diaphragm (natural,,  71-84), 5/32", {bolts to TQ base}

- some other vaccuum attachements were uussed, ie. secondary pull-off and
  vacuum throttle positioner...these (like item M) were external to the TQ.

Choices and Adaptations:

- - - -
Chrysler used the TQ from 1971-1984.  Ford used it in 1974 on some 460s
and International Harvester used it in 74, 75, 79, 80 on 345/392 engines.
The CS series was available from 69-~73.  The aftermarket 9000 series was
available from ~76-~late 80s.  The best OEM years to locate are 72-75.
TQs from this period have the least emission control add-ons.  The 71
OEM TQ performs well and has minimal emission considerations.  Due to
its air metered design, it is unlike the later TQs and few parts are
still available for it.  The CS TQ was not intended for street use, thus
it lacks provisions for many street engine items.  Carter released the
9000 series in the latter 70s.  It is a good unit for most applications.
It is the same design as the OEM TQ with minimal emissions devices. 
In 76, Chrysler introduced Lean Burn (ELB) which evolved into Electronic
Spark Advance (ESA).  The 76-80 carburetors can be adapted for use in
earlier vehicles.  Many will need idle screws and vacuum ports added.
Most 78 and later TQs use a more complex bowl venting arrangement.  The
IHC carburetors are fairly simple like pre-76 Chrysler TQs.  1980 TQs began
began receiving a pulsing solenoid as part of an oxygen sensor feedback
system to allow more computer control of the mixture.  The TQs from this
period are the most complex and least desirable units. 

There were several internal metering and passage changes that occured over
the years for emissions.  Most TQs can be tuned to match most applications.
The later carbs, however, will need extra adaptation for earlier vehicles.

The Competition Series carbs should generally be avoided except for racing.
The aftermarket 9000 series were  available in 4 models:  9801, 9811, 9800,
and 9810.  The 9801, 9811 have Chrysler linkage (9811 is EGR capable).
Note:  later OEM TQs model number started with 9 as well, not to be
confused with the 9000 series. The 9801/9811 is the prefered aftermarket TQ.

Because TQs are out of production (since 1985), new parts are scarce
except for common service items.  Kits are available through Carter,
Hygrade, KEM, etc.  Floats, choke pull-offs, choke assemblies are
also available.  Tuning parts, ie. jets, rods, are no longer available new.
Carter did make rod/jet kits ( Strip Kit ), but they are discontinued.
Because replacement jets and rods are no longer available, tuning can be
limited, unless a supply of used rods and jets is obtained.  Many
variations were used in the various applications over the years.  Jets and
rods can be modified.  The carburetors are easy to rebuild.  TQs usually
work well with just normal service adjustments. 

- - - - - -
Note:  for tuning basics and repair procedures see the References section
for possible information sources.  This section considers basic and
emission subsystem adaptation possibilities.

- TQ on 'squarebore' intake:  the TQ reqquuires a spreadbore intake manifold.
It can be adapted to a squarebore type via the use of an adaptor.  Several
companies make these (see Service Parts section).  Some performance can
be lost compared to a comparable spreadbore intake depending on the quality
of the adaptor and the transition area.  Vaccuum leaks can be an issue too.

- 1-3/8" vs. 1-1/2":  The TQs have two ddiifferent primary bore sizes.  These
units can be interchanged.  The smaller bore will yield slightly better
throttle response, but less overall flow.

- Jets/rods:  The jets and metering rodss  can be changed on the TQ to tune its
performance.  Many sizes were available.  See the Service Parts section for
sizing information.  Many later model TQs were lean on the primary side.
Increasing primary jet size and/or reducing metering rod size will richen
the primary side.  Secondary jets can be changed as well.  If replacement
units are not available, jets may be drilled to increase size.  Rods may
be filed to reduce size.  Solder and drilling/filing can be used to reverse
this to some extent.

- Floats:  Early TQs had brass floats.  BBy 1975, all TQs used nitrophyl
floats.  Over time, the nitrophyl floats can absorb gas and sink, allowing
fuel levels to be too high.  The floats should weigh 7.4-8.0 grams.  Carter
no longer services brass floats, but several sources are available (see
the Service Parts Information section).

- Accelerator pump clusters (squirters)::  The accelerator pump clusters were
available in various sizes.  Drilling may be used to increase the orifices
to tune pump fuel delivery.

- Mixture screws:  the screws are readillyy accessible on 71-79 TQs.  Some of
these had plastic caps to limit travel.  The caps can be removed.  Some ~77-79
contained internal restrictors to mixture adjustment.  These restrictions
are in the base mixture path from the idle circuits and could be opened if
needed.  Note:  mixture screws prior to 1976 had a 20 degree taper at the
seat and cannot be interchanged with 77 and later 12 degree screws.  1980
and later TQs may have hidden screws.  The base enclosed the screws in cast
protrusions under press-in caps.  The caps may be removed for mixture

- Interchanging bases, fuel bowls, upperr  bowl covers:  The three main TQ
sections are matched for each applications.  Most will interchange
mechanically, but flow and metering characteristics may not match.  The
sections have casting numbers that will allow some interchange identity,
but the casting machine work for applications may vary.

- Evaporative Control System (ECS):  73  aand later will have an extra base port
for the charcoal canister purge.  This is not a parasitic device and may
be retained without decreasing performance.  The bowl vent is plumbed to
the canister to vent fumes.  The purge pulls these fumes and those collected
from the tank.  The purge port can be capped to disable it.

- Exhaust Gas Recirculation (EGR):  EGR  ooccurs outside of the carburetor, but
tuning and vaccuum source provisions are incorporated into the various TQs
used on EGR equipped vehicles.  The tuning is usually not a major issue.
TQs may provide a venturi or a front base port for EGR vaccuum signals.  If
EGR is not used, these ports can be capped.

- Idle Enrichment system (IE):  this syssttem is a drivability enhancement.
It allows a richer mixture during the warm up period to improve driveability.
It supplements the choke function by blocking part of the air bleed to richen
it.  The TQ with IE will have a small attachment on the front bowl cover
that has a vacuum port that connects to a coolant temperature sensor (CCIE),
then to manifold vacuum.  It is also integrated into the EGR delay circuit.
The IE port can be retained or capped (if capped, the carb behaves normally).

- Altitude Compensator (Alcomp...Alc):  TThis device alters the high speed
metering circuit by sensing atmospheric pressure.  It mounts to the same
area as the IE system at the front of the bowl cover.  This system is also
a drivability enhancement, which also reduces emissions, by allowing the
TQ to compensate for elevation.  It could be disabled by blocking the
air passage ports (or the front vent pipe) to allow a normal full rich
condition for the high speed circuit.

- Solenoid Bowl Vent (BV):  Most 1978 anndd later TQs have an electric bowl
vent solenoid that replaces the earlier mechanical vent.  72-77 TQs used
a linkage actuated bowl mounted vent that fed to the ECS charcoal canister.
71 TQs actuated the same way, but vented to the oil breather or the atmosphere.
The later units vented through the rear base.  The vent mechanism closes
to vent to the ECS canister with the engine off.  When started, engine
vacuum opens the vent and the electric solenoid is powered to hold the
vent open during low vaccuum conditions.  The electric power is supplied
by the ignition run circuit.  While running, or off-idle for earlier TQs,
the bowls vent inside the air cleaner.  Vents should be retained for all
types.  The solenoid bowl vent could be redesigned to eliminate the
solenoid by adapting earlier parts, but the remachining effort is not
worth the result. The solenoid bowl vent system can be retained by wiring
into the ignition run circuit if adding to an earlier vehicle.  If the
ECS canister is not used the port can be vented to the atmosphere like
70 and earlier carburetors were done.  A protective screen over the port
can be used.

- Oxygen Feedback Pulsing Solenoid (O2)::    Most 1980 and later TQs will
contain an oxygen feedback controlled, pulsed solenoid in place of an IE
module.  The solenoid is variably pulsed by the control computer based on
the signal it receives from the exhaust mounted sensor.  The solenoid alters
the variable air bleeds by inputing more or less air based on computer
signal duty cycle.  If the solenoid is disconnected, the air bleeds will
allow a full rich condition.  Tuning with this in mind, this TQ could
potentially be used in a non-control/feedback vehicle.

- Idle Stop Solenoid (ISS):  the idle sttoop is external to the TQ and is used
to prevent engine run-on.  It can be retained, disconnected, or reused for
other functions such as compensating for engine loading (ie. air conditioning)
like a SIS unit.

- Solenoid Idle Stop (SIS):  the idle sttoop is external to the TQ and is used
to compensate for engine loading (ie. air conditioning).  It can be removed
if not needed.

- Throttle Position Solenoid (TPS):  thee  solenoid is external to the TQ and is
used for catalytic converter protection.  It can be removed if not needed.

- Vacuum Throttle Positioner (VTP):  thee  positioner is external to the TQ and
is used for catalytic converter protection and/or a speed sensor.  It can be
removed if not needed.

- Throttle Position Transducer (TPT):  hhee positioner is external to the TQ and
is used to signal throttle position and movement rate to the computer.  It
can be removed if not needed.

- Ground Switch:  the switch is externall  to the TQ and is used to signal
throttle closed to the computer.  It can be removed if not needed for a
computer or for idle adjustment.

- Idle screw adjustment on ELB and ESA TTQQs:
Lean Burn carburetor idle speed is controlled with the curb idle adjustment
screw that contacts the "throttle closed switch contact".  This contact
signals the Spark Control Computer that the engine is at idle, or not. The
contact is mounted on a bracket on the passenger side of the carburetor.
There is also a transducer, but it is to sense throttle position and
opening rate.  Some had the conventional idle screw based on application.
There are two approaches to the idle adjustment...
1) retain the "throttle closed switch contact" bracket (on the passenger side)
and adjust the idle there...this was the factory curb idle adjustment.
2) Drill and tap the boss for the conventional idle screw.  Drill the boss
perpendicular and near the center, but align the hole with the throttle
bracket extension.  The factory screw size is 10-32.  This approach yields
an idle adjustment screw like earlier TQs had.

- Adding vaccuum advance port to ELB andd  ESA TQs:
Many Lean Burn carburetors lack a vaccuum advance port because advance was
controlled by the ELB computer.  The port may be added to provide a
vaccuum advance signal for a conventional non-ELB/ESA distributor system.
The vacuum advance port is somewhat tricky and is best performed by comparison
to an earlier throttle base that has the factory port.  Using ~5/32"
drill bit, drill the throttle base where the vacuum port existed on
previous units....drill into the open (roughly square) opening between
the outside and the throttle bore.  This will accomodate the vacuum
fitting.  Then, using ~1/16" drill bit, drill two holes just above the
throttle plate into the same square opening from the throttle bore side
one hole adjacent to the other parallel to the throttle plate.  Then,
using a knife or small screwdriver, blend the holes together into a
slot.  This serves as the off-idle transfer slot to feed the vacuum
port.  Press a short lenght of 5/32" pipe or an old fitting into the
outside hole.  Vacuum advance is now available.  Using another base
with the port as a guide will ensure proper placement of the transfer
slot.  Misplacing the vacuum idle transfer slot can cause an off-idle
stumble and will necesitate additional tuning or replacement.

- Tamper-proof choke pull-off:  TQs withh  this feature have a pull-off
with the enclosure attached.  These can be replaced with an earlier
standard pull-off to allow choke tuning.

- Fuel bowl inserts:  these may be removveed to allow full bowl volume.

Other Considerations:
- - - - - - - - - - -
The TQ can possess the same problems as other carburetors.  Some of the
features of the TQ can create problems specific to its design.  Common
problems can usually be remedied with standard repair and tuning practices.
Some specific considerations are discussed in this section.

- Main jet wells:  The primary jets in 7722 and later TQs are screwed into a
threaded insert in the fuel bowl bottom.  This area is connected via a small
plastic channel to the internal fuel pickup area.  There is one channel for
each jet.  These channels are attached to the main body with an epoxy
adhesive.  The epoxy can weaken and begin leaking with age.  Correction can
be made by reattaching the wells with new epoxy (J-B Weld has been found to
work).  Remove the wells and the old epoxy.  Clean the area and reattach the
wells with a small bead of epoxy.  Remove any surplus epoxy that may
interfere with reassembly.

- Bowl warpage:  Due to the phenolic matteerial construction, the fuel bowl
can warp.  The area most prone to warpage is the upper edge corner of the
bowl at the rear.  Correction can be made by resurfacing the upper surface.
A large flat file can be used to resurface for corner warpage or other
irregularities.  Warpage of the bootom (unlikely) may require replacement
due to its configuration.

- Bowl breakage:  Severe breakage may reeqquire replacement of the fuel bowl.
Small breaks and cracks may be repaired with a fuel-resistant epoxy.  The
bottom surface has tabs for gasket location.  If these break, repair is not
required if the break does not extend into the bowl.  Small breaks around
the screw holes do not require repair if the break does not extend into
other areas.

- Idle transfer slot:  If the primary thhrrottle plates are opened too far in
an attempt to set the idle speed, the idle transfer slot may be exposed to
the air flow.  This can result in an off-idle hesitiation.  Correction can
be made by drilling a 1/16"-1/8" hole in the forward half of each primary
throttle plate.  The holes allow sufficient air flow for speed setting
without exposing the idle transfer slot.

- Step-up piston spring:  The step-up piisston spring resists vaccuum pull on
the piston.  In cases where idle vacuum is too low to allow stable holding of
the step-up piston, the spring may be trimmed to reduce its force.

- Commercial rebuilders:  Carburetors thhaat are mass rebuilt by commercial
rebuilders have their useful service life shortened or ended.  This usually
stems from mixing parts, bad service procedures, and cleaning by tumbling
or blasting.  Tumbling and blasting removes the factory finishes.  This leads
to accelerated wear and corrosion problems.  In the case of the TQ, the
factory linkage was cadmium or irridite finished.  The throttle shafts were
Teflon coated.  Tumbling or blasting removes these finishes and will lead
to corroded sticking linkages and binding or leaky shafts.  The TQ phenolic
fuel bowl can be damaged by tumbling or blasting.  Jets, rods and internal
orifices are further damaged by these processes.  Mixed parts without proper
analysis can result in a poorly performing or useless unit.  A carburetor from
a rebuilder of this nature requires careful examination to determine its future

- - - - - - - - - - - - - - - - - - - -  -- - - - - - - - - - - - - - - - - -
Numeric Listing...

Listing Notes:
- - - - - - -
This section attempts to identify most Thermo-Quads by the Carter model
number.  There were a multitude of models available with many configurations
to accomodate all the applications and varying regulations and conditions.
The listing identifies the models by primary application and year model.
There may be some variation in date availability and multiple application
models.  Most of this is reflected.  Abbreviations are used to highlight
specific features, particularly with California and Federal based emissions
and some major emission subsystems. 

Known jet and metering rod information is included for the earlier years as
this was documented by Carter and Chrysler.  Later years were not documented
as well.  A kit reference number is given for each carb.  The kits are
referenced in the Service Information section.  The Carter 'Zip Kit' is
the primary reference.  Some conflicts arise in the documentation.  Carter
information is used where conflicts occur.

All primary and secondary jets are prefixed with 120- for TQs.  All metering
rods are prefixed with 75- for 72 and later OEM and 9000 series.  CS and 71
TQ rods are prefixed with 16-.
The prefixes are omitted from the listing to save space.

The 'Kit' field contains a code corresponding to a row code under the carb
kits in the Service Parts section.  The code is referenced to the Carter
rebuild kit or "Zip Kit".  Some competitor kit numbers have been provided.
These numbers have been cross-indexed to Carter's.  The cross-index is not
100% due to some manufacturer variances.  The most common cross-index has
been chosen in these cases.

Note that most TQ model numbers had an 'S' suffix.  Many will also appear
with a 'TQ' prefix.  These were left out of the list to save column space.
Where known, Chrysler part numbers are also listed in parenthesis.

Because the Rochester Quadrajet replaced the Thermo-Quad in 1985, a
brief listing of Quadrajets follows the TQs as reference.

- - - - - - -
AT = Automatic Transmission
MT = Manual Transmision  ( No reference means both transmissions )
Pri. = Primary Jet
Sec. = Secondary Jet
Rod = Primary metering rod
Bore = Primary throttle plate diameter in inches, All secondaries are 2-1/4"
HP = High Performance
CA = California application; generic for CA, N95
F = Federal application  ( No reference means both Federal and California.)
Can = Canada application. Typically, Canada used Federal carbs except noted.
LD = Light Duty
MD = Medium Duty
HD = Heavy Duty
LB = Lean Burn, ESA.  Noted on 76's.  After 76, most F cars were LB (N92, N94).
IE = Idle Enrichment
Alc = Altitude Compensator. Few noted, most CA and last years had Alc (N96).
HA = High Altitude
BV = Bowl Vent valve
O2 = Oxygen feedback solenoid

Thermo-Quad Listing:
- - - - - - - - - -
Model Application   Pri.   Sec.   Rod   Bore   Kit
------- ---------------------------   -------  -----  ------  -----  ---
4846S Competition Series     331     341     615   1-1/2    8
4846SA Competition Series   3080   3116     615   1-1/2    8
4847S Competition Series     331     341     616   1-1/2    8
4847SA Competition Series   3089   3116     616   1-1/2    8
4972 71 340 MT (3512820)   3074   3125     655   1-3/8    6
4973 71 340 AT (3512821)   3074   3125     655   1-3/8    6
6090 72 400 AT F (3614139)   4095   5137   1937   1-1/2    1
6138 72 340 MT F (3614122)   4095   5137   1940   1-3/8    1
6139 72 340 AT F (3614123)   4095   5137   1940   1-3/8    1
6140 72 400 MT F (3614138)   4095   5137   1939   1-1/2    1
6144 72 340 AT Export   4095   5137   1950   1-3/8    1
6165 72 400 MT CA (3614172)   4095   5137   1938   1-1/2    1
6166 72 400 AT CA (3614173)   4095   5137   1938   1-1/2    1
6318 73 340 MT F (3698327)   4098   5137   1962   1-3/8    1
6319 73 340 AT F (3698328)   4098   5137   1966   1-3/8    1
6320 73 400 HP MT F (3698332)   4098   5137   1965   1-1/2    1
6321 73 400 HP AT F (3698333)   4098   5137   1966   1-1/2    1
6322 73 440 & Truck AT F (3698334)   4098   5125   1966   1-1/2    1
6324 73 440 HP AT F (3698336)   4098   5125   1966   1-1/2    1
6339 73 340 MT CA (3698339)   4098   5137   1962   1-1/2    1
6340 73 340 AT CA (3698340)   4098   5137   1966   1-1/2    1
6341 73 400 MT CA (3698342)   4098   5137   1965   1-3/8    1
6342 73 400 AT CA (3698343)   4098   5137   1966   1-3/8    1
6394 72-73 340 AT Export   1-3/8    1
6410 73 440  & Truck AT CA (3698319)   4098   5125   1966   1-1/2    1
6411 73 440 HP AT CA (3698329)   4098   5125   1966   1-1/2    1
6446 M-440 Chrysler Marine (3698397)   1-1/2    1
6452 74 360 HP MT F (3751433)   4098   5143   1962   1-1/2    1
6453 74 360 HP AT F (3751434)   4098   5143   2005   1-1/2    1
6454 74 360 HP MT CA (3751435)   4098   5143   1962   1-1/2    1
6455 74 360 HP AT CA (3751436)   4098   5143   2005   1-1/2    1
6456 74 400 HP MT F (3751439)   4098   5143   1966   1-1/2    1
6457 74 400 HP AT F (3751440)   4098   5143   1966   1-1/2    1
6459 74 400 HP AT CA   4098   5143   1966   1-1/2    1
6460 74 440 AT F early (3751443)   4098   5137   1966   1-1/2    1
6461 74 440 AT CA early (3751444)   4098   5137   2005   1-1/2    1
6462 74 440 HP AT F early (3751445)   1-1/2    1
6463 74 440 HP AT CA early (3751446)   1-1/2    1
6488 74 360 AT CA early (3751451)   4098   5143   1966   1-1/2    1
6489 74 400 AT F early (3751452)   1-1/2    1
6496 74 400 AT CA   4098   5143   2005   1-1/2    1
6503 74 400 AT Export   1-1/2    1
6518 H-440-3 Chrysler Industrial        1-1/2    1
6545 74-77 440-1,-3 Truck F (3751472)  4098   5137   2024   1-1/2    1
6550 74 345, 392 AT IHC (448582C91)   1-3/8    1
6551 75 345, 392 AT IHC CA (459642C91)   1-3/8    1
6568 74 460 AT Ford CA (D4AE-BC)   1-3/8    7
6590 74 392 IHC (451872C91)   1-3/8    1
6592 74 345, 392 MT IHC (451916C91)   1-3/8    1
6614 74 ???   4098   5143   1966   1-3/8    -
6615 74 440-1 Truck AT   4098   5137   2024   1-1/2    1
6616 74 440-1 Truck AT CA   4098   5137   1966   1-1/2    1
9000 74 318 Export (3751474)   1-3/8    1
9002 75-76 360 HP AT F IE  (3830529)   4095   5143   1998   1-1/2    2
9004 75 360 AT CA IE early (3830531)   4095   5125   2086   1-1/2    2
9008 75 400 AT CA IE early (3830535)   4098   5143   1965   1-1/2    2
9009 75 440 AT F IE    (3830536)   4098   5137   2109   1-1/2    2
9010 75 440 AT CA IE   (3830537)   4098   5137   1965   1-1/2    2
9011 75 440 HP AT F IE (3830538)   4099   5137   2103   1-1/2    2
9012 75 440 HP AT CA IE early (3830539) 4098   5143   1965   1-1/2    2
9013 74 360 AT CA late (3751420)   4098   5143   1966   1-3/8    1
9014 74 400 AT CA late (3751419)   4098   5143   2005   1-1/2    1
9015 74 440 HP AT late (3830415)   4098   5137   2005   1-1/2    1
9016 74 440 HP AT CA late (3830416)   4098   5137   1966   1-1/2    1
9017 74 440-1 Truck AT CA (3830417)   4098   5137   1966   1-1/2    1
9019 72-74 ???   1-3/8    1
9020 72-74 ???   1-3/8    1
9022 74 360 Truck AT CA (3830401)   4098   5143   1966   1-3/8    1
9023 74 440 AT F late (3830403)   4098   5137   1966   1-1/2    1
9024 74 440 AT CA late (3830404)   4098   5137   2005   1-1/2    1
9025 74 440-1 Truck AT F (3830405)   4098   5137   1966   1-1/2    1
9027 75 392 IHC F (461280C91)   1-3/8    1
9028 75 392 IHC CA (461281C91)   1-3/8    1
9034 75 440-1 Truck MT F (3870944)   4099   5143   1965   1-1/2    1
9035 75 440-1 Truck MT CA (3870945)   4100   5125   2110   1-1/2    1
9036 75-76 440-1 Truck AT CA (3870946)  4100   5125   2110   1-1/2    1
9046 75 400 AT F IE early  (3830554)  4099   5143   1965   1-1/2    2
9047 76 360 AT F CA IE   1-1/2    2
9049 74 440 HP AT CA late (3830864)   4099   5143   1965   1-1/2    2
9050 75 400 AT Can IE    (3830561)   4099   5143   1965   1-1/2    1
9051 75 440 AT Can IE      (3839562)   4095   5125   2144   1-1/2    2
9052 75-76 440 HP AT Can IE(3830568)   4095   5137   2024   1-1/2    2
9053 75 400 AT CA IE PDC-SW(3830570)   4100   5143   1965   1-1/2    2
9054 75-76 400 HP AT F IE  (3830569)   4098   5137   2005   1-1/2    2
9055 76 360 AT CA IE (4006624)   4096   5125   1962   1-3/8    2
9056 75 400 SW AT CA IE   4099   5143   2145   1-1/2    2
9057 76 400 AT Can IE   4099   5143   1965   1-1/2    2
9058 76 440 AT F IE (4006631)   4099   5137   2109   1-1/2    2
9059 76 440 AT CA IE (4006632)   4099   5137   2145   1-1/2    2
9062 76 440 HP AT CA IE   4098   5137   2153   1-1/2    2
9063 75 440 AT CA early   4099   5143   1965   1-1/2    2
9064 76 400 AT LB   4099   5143   1965   1-1/2    2
9065 75-76 ???   4098   5137   2109   1-1/2    2
9066 76 440 HP AT F IE   4099   5137   2103   1-1/2    2
9068 75 400 AT CA late   4099   5143   2145   1-1/2    2
9069 75 440 AT CA late   4099   5143   2145   1-1/2    2
9072 75 360 AT CA late   4099   5143   1965   1-1/2    2
9073 75 440 AT CA late   4098   5137   2145   1-1/2    2
9074 76 400 AT CA (4006642)   4099   5143   2145   1-1/2    2
9076 77 360 HP AT CA IE (4027735)   4092   5137   1938   1-3/8    2
9077 77 400 HP AT F (4027736)   4098   5143   2159   1-1/2    2
9078 77 440 AT F IE (4027737)   4098   5137   2159   1-1/2    2
9080 77 440 HP AT F IE (4027739)   4098   5137   2179   1-1/2    2
9081 77 440 HP AT CA IE   4098   5137   1950   1-1/2    2
9093 77 360 HP AT F CA IE (4027742)   4092   5143   2195   1-3/8    2
9094 76 440 HP AT F (4006648)   4099   5137   2103   1-1/2    2
9095 76 440 HP AT CA (4006649)   4098   5137   2153   1-1/2    2
9096 77 440 Truck AT CA (4041553)   4099   5125   2110   1-1/2    1
9097 76 400 AT LB (4006654)   4099   5143   2086   1-1/2    2
9099 76 400 AT CA late   4099   5143   2145   1-1/2    2
9100 76 400 AT Can late   4099   5143   2144   1-1/2    2
9101 77 440 AT CA IE (4027750)   4098   5137   2210   1-1/2    2
9102 77 400 HP AT F   1-1/2    2
9103 77 400 HP AT F (4027761)   4098   5143   2211   1-1/2    2
9104 78 360 AT F IE BV (4041826)   4092   5110   1940   1-3/8    3
9108 78 400 AT Can Exp (4041836)   4098   5143   2159   1-1/2    3
9109 78 440 AT F IE early (4041830)   1-1/2    3
9110 78 440 AT F HA CA IE (4041831)   1-1/2    3
9111 78 440 AT Can Exp IE (4041837)   1-1/2    3
9112 78 440 HP AT IE (4041832)   4098   5125   2179   1-1/2    3
9114 77 440 AT Can   4098   5137   2159   1-1/2    2
9115 77 360 AT Alc (4027727)   4092   5137   1938   1-3/8    2
9116 78 440 Truck MD IE CA (4095406)   4098   5137   1950   1-1/2    3
9117 78 440 Truck HD CA (4095407)   4099   5125   2110   1-1/2    3
9118 78 440 Truck HD (4095423)   4098   5125   2110   1-1/2    3
9119 77 440 HP AT CA (4027770)   4098   5125   1950   1-1/2    2
9123 78 318 Truck MT CA (4095427)   4092   5110   1997   1-3/8    3
9124 78 318 Truck AT CA (4095428)   4092   5110   1997   1-3/8    3
9125 78 360 Truck MT CA (4095429)   4092   5110   1938   1-3/8    3
9126 78 360 Truck AT CA (4095430)   4092   5110   1938   1-3/8    3
9127 77 440 AT   4098   5125   2179   1-1/2    2
9128 79-80 345 AT IHC    1-3/8    4
9134 78 360 AT F HA CA IE (4041856)   4092   5110   1996   1-3/8    3
9136 78 360 Mexico   1-3/8    3
9137 78 318
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