Gathering of the Green 2008 Winter Convention



Gathering of the Green 2008 Winter Convention
Gathering of the Green
2008 Winter Convention
March 12 - 15
Moline, IL
Carburetors: History, Application and Servicing
Wheeler Schebler D
Marvel Schebler TCX, TSX
DLTX 1 barrel
DLTX 2 barrel
Duane Larson
Knoxville, TN
• Carburetors require periodic servicing and
repair to properly perform their function
– Provide the proper mixture of fuel and air, in
the proper amount, to the engine
• Workshop has been led by Bob Beaver of
Roberts Carburetor Repair
• I have researched and rebuilt carburetors
and magnetos for over 25 years
– Got “volunteered” to lead this workshop
Acknowledgements and References
• Several folks have answered my call for
Bob Beaver
Steve Ridenour and Jack Kreeger – Y, 62
Kent Pribil – Spoker D (leading workshop)
J. R. Hobbs – Nice books on Unstyled and Styled
Deere tractors
• References
Carburetor manuals
Deere parts books and SM-2024 Carb Manual
Carburetors and Carburetion – Walter Larew
Field Service Bulletins
• Handout available – Application Chart
Handouts from the Gathering of the Green workshops are among
the information included on the CD available through this web site.
Outline of Talk
• History of the carburetor companies
– Wheeler-Schebler, Marvel, Ensign, Zenith
• Identify the various types of carburetors
– Air valve, plain tube, updraft..
• How carburetors work
– Study systems which make up a carb
• Fuel, idle, load, acceleration, economizer..
Outline of Talk
• Discussion of particular carburetors
– Schebler D series used on Waterloo Boy, D
– Marvel Schebler
• DLT 1 barrel
• DLT duplex (2 barrel)
– Ensign
• Covered by Cork Groth in his Workshop
• Repair suggestions with each series
Deere Carburetor History
• Carburetors all follow from WheelerSchebler and Marvel linage
– Two exceptions
• Ensign Bj and Kj series used on GP, few D’s
• Zenith TU series used on diesel starting engines
• George Schebler and Burt Pierce
– Fiddle makers/woodworkers in Indianapolis
– Developed two carburetor styles
– Flipped coin
• Schebler pursued Air-valve design
– Patent 1902
• Pierce pursued “Marvel” design
– Patent 1909
Deere Carburetor History
• Frank Wheeler funded Schebler design
– Formed Wheeler-Schebler ~1905 (1901?)
– Built new facilities 1911
– Wheeler bought out Schebler in 1914 for $1m
• Sugar futures in WWI – both lost fortunes
– Wheeler died May 1921
– Schebler died November 1942
• Wheeler-Schebler very successful
– Carburetors used on all Waterloo Boys and Ds
– Factory still standing – Wheeler Arts Center
Wheeler-Schebler Model D Carburetor
Gas Review November 1913
Used on tractors, boats, and stationary
engines, including the Waterloo Boy
and Model D tractors
Gas Review September 1917
Deere Carburetor History
• Marvel Carburetor Company formed 1908
– J. R. Francis funded Burt Pierce’s Marvel design
– Sales to the new General Motors increased
• Marvel moved to Flint MI in 1912
• Pierce sold interests, became consultant
– Developed carburetor cleaner - Marvel Mystery Oil
– 6000 carburetors/day produced in 1928
• Marvel bought Wheeler-Schebler March 1928
– Wheeler Schebler operations moved to Flint July 1931
• Borg-Warner company formed June 1928
– Four companies, including Marvel
• Designated Marvel-Schebler Division in 1934
Deere Carburetor History
• Marvel Schebler moved to Decatur, IL 1948
– Opened new factory October 1950
• Borg Warner sold Marvel Schebler carburetor line
to Facet Enterprises in 1982
– Decatur plant closed April 15, 1983
• Facet sold Marvel Schebler product line to Zenith
Fuel Systems 1990
• Comment on Schebler model identification
– Start with Schebler D series
• Evolved to Schebler DL (DeLuxe) plain tube motorcycle series
– Evolved to DLT (Tractor) plain tube series for Deere
– DLTX used by Deere, where X is part of the part number
Deere Carburetor History
• Ensign Carburetor Company
– Formed in 1911 by Orville H. Ensign
• Huntington Park, CA (near Los Angeles)
• First carburetor based on 1912 patents
– Tractor customers included
Holt and Caterpillar
Hart Parr/Oliver
John Deere
– Transitioned to LP-Butane carburetors in ’40’s
– Sold to American Bosch 1960
– Hard to find carburetor parts or literature
Deere Carburetor History
• Zenith Carburetor
– Based on French design of M. Baverey
– Licensed to Zenith-Detroit Corporation
• Began building carburetors in 1909
• Purchased by Bendix Aviation February 1935
– Vincent Bendix invented the Bendix starter
– 1930’s sold carburetors to most tractor builders
– R20TP line used on both Novo and Hercules
engines in Model Y Wagon Works tractor
– TU line used on diesel starting engines
– Company in business as Zenith Fuel Systems
• Provide some Marvel Schebler parts
Carburetor Types
• Different basic designs used by Deere
– Air Valve carburetor
• Wheeler Schebler D
– Used on Waterloo Boy and early D’s
• Has no venturi
• Air valve and spring operation critical
– Plain Tube carburetor
• Also called Natural Draft, Single- or Dual-Induction, or
Straight Through carburetors
• Schebler DLT series
– Waterloo letter and number series tractors
• Uses a venturi
Carburetor Types
– Updraft carburetor
• Schebler TCX, TSX series
– L, LA series, Dubuque series tractors
– Downdraft carburetor
• Zenith TU series
– Diesel Starting Engines
– Mixing Valve (too simple to be called a carb)
• Marvel Schebler SL-2
– R diesel starting engine
– LP carburetors
• Schebler TSG series for Dubuque series
• Deere carburetors using MS parts for Waterloo
Principles Applicable to all Carburetors
• A carburetor must do two things
– Control amount of fuel/air mixture to cylinders
• Position of the throttle plate
– Control the ratio of fuel to air in the mixture
• Opening of load and idle needles
• Vapor mixture about 2% fuel, 98% air
• Nebraska Test 222 1934 A Rated Load test
– Used 5.6 gal air and 0.5 teaspoon fuel in one second
» Equivalent to 0.11 gal fuel vapor
How Carburetors Work
Calvin and Hobbes by Bill Watterson
Well, lets see if we can figure it out……
How Carburetors Work
• It’s all due to Air Pressure (or lack thereof)
• Close to sea level pressure is 14.7 psi
– Air has weight – 88 lbs in a 12x12x8 ft room
• “Vacuum” is a pressure less than 14.7 psi
– Often measured in inches of mercury
• 14.7 psi ~ 30 in Hg
• As engine runs, intake strokes create
“vacuum” or lower air pressure in manifold
– Normal ~10 psi (~20 in Hg)
• With throttle plate open, carburetor throat
exposed to manifold pressure
How Carburetors Work
• Carburetors operate on the venturi effect
• The venturi is a narrowing of the bore
How Carburetors Work
• What causes air flow through carburetor?
– Intake stroke of piston creates vacuum
• Intake valve open, transmits vacuum to throttle
– Position of throttle plate determines air flow
• Closed – no flow – high manifold vacuum
• Open – full flow – low manifold vacuum
– Air (at ~ atmospheric pressure) flows from air
cleaner side, through venturi, past throttle
plate, through manifold and intake valve, into
• Model A running at 975 rpm flows about 70 cfm
How Carburetors Work
• As air flows through venturi, pressure decreases in
– Bernoulli’s Law tells us as Area decreases, velocity
• and
– As velocity increases, pressure decreases
• Air pressure on fuel in bowl is always ~atmospheric
• As pressure difference between 1) fuel in bowl and
2) at tip of nozzle (located in venturi) increases, fuel
flow increases from nozzle
– Throttle opens, more air flow, greater ∆P, more fuel flow
– Throttle closes, less air flow, less ∆P, less fuel flow
How Carburetors Work
• Important factors
– Amount of vacuum created by intake stroke
• Less vacuum if
Intake valve guides leak air
Exhaust valve leaks air
Piston rings leak air
Manifold gasket leaks air
– Position of throttle plate
• Determines air flow through carburetor
– Determines difference in pressure on fuel in bowl and at
tip of nozzle in venturi
» Greater difference – more fuel flow
How Carburetors Work – Throttle system
% Bore Open
% Bore open = πb²(1 - cosθ)x100
“Bore Open” is difference between bore
size and area of throttle plate
b = radius of bore size
How Carburetors Work
• Venturi region
– Bernoulli’s Law tells us as
Area decreases, velocity
– and
– As velocity increases,
pressure decreases
Incoming air 14.7 psi
Venturi pressure 8 psi
Outgoing air ~10 psi
Pressure difference
14.7 – 8 = 6.7 psi
• So fuel flows out of venturi
into the air stream to the
manifold and cylinders
To manifold
How Carburetors Work – Necessary systems
• Previous carburetor fine for fixed speed
hit ‘n miss engine
• Refinements needed for tractor carburetor
– Fuel supply system
• Means of maintaining correct fuel level in bowl
– Choke system
• Means of regulating amount of air for starting
– Throttle system
• Means of regulating amount of fuel-air mixture
– Idle system
• Means of supplying just enough fuel-air mixture to
run with no load
How Carburetors Work – Necessary systems
– Load system
• Means of metering correct fuel-air ratio above idle
– Accelerating system
• Provide adequate fuel when throttle opens quickly
– Economizer system
• Retards fuel flow at part throttle speeds
• Solves common carburetor design problem
• Look at these seven systems on a Marvel
Schebler DLT series one barrel carburetor
– Simple example and a popular carburetor
How Carburetors Work – fuel supply system
• Fuel flows through a strainer
to the needle and seat, then
to the fuel bowl
• Seats are brass, needles
have steel tips (viton
• Fuel level – measure with
1/8”NPT fitting in bowl drain
hole, and clear plastic tubing
– All DLTX except 67-73
• 3/4” down from bowl gasket
– DLTX67-73
• 5/8” down from bowl gasket
• Bowl baffles allow higher level
How Carburetors Work – Choke system
• Used for starting and
• Manifold is cold
– Only volatile parts of fuel
– Need more fuel
• Choke restricts air flow
– Further reduces venturi
• Produces more fuel flow
• Slot on choke lever
always parallel to plate
Choke Plate Locating Line on Choke Lever
Line always parallel to choke plate position
How Carburetors Work – Choke system
• Waterloo Boy’s did not have choke system
• Not functional for starting on D’s built before
109944 (Nov 1, 1930)
• Spring-loaded choke lever and choke plate in
place, but…..
– Had no mechanism in place to operate during starting
– Instruction manuals make no reference to use
– Starting instructions are to use 1 tablespoon High Test
gasoline in each petcock
– Would have to use wire to hold open – none furnished
– Useful after starts to choke by hand until warms up
How Carburetors Work – Throttle system
• Throttle plate
– Regulates amount of fuelair mixture entering
– Regulates amount of fuel
in mixture
– Varies engine speed
• Governor connected to
throttle plate and speed
control lever
– Governor maintains rpm
– Increase load, governor
opens throttle plate to
maintain rpm
How Carburetors Work – Idling System
• Slow idle – throttle shut
• Provide fuel-air to keep
engine running
– Primary idle hole sees manifold
– Air enters, picks up fuel at idle
needle, mixture goes out
primary hole
• Air enters secondary hole
• Fast idle – both holes open –
richer mixture
• Good system – works under
high suction, mixture flows at
high velocities in small
DLT Idle Circuit Passages
Idle Circuit
How Carburetors Work – Idling System Problems
• Unmetered air
– Worn shaft bushings
– Bushings not fitted to
throttle plate
– Brass plug threads
– Idle needle threads
• Plugged passages
– Air entry into idle needle
– Small passage at
bottom of idle needle
– Primary and secondary
– Remove all brass plugs,
ream to size
How Carburetors Work – Accelerating System
• At idle, no venturi flow
• Fuel rises in nozzle by load
needle to level in fuel bowl
• Holes in nozzle let fuel flow
into cavity around nozzle
– “accelerating well”
• Open throttle rapidly
– Venturi effect
• Fuel flows thru nozzle
• Also from accelerating well
thru holes in nozzle
• Accelerating well provides
necessary extra fuel for
richer fuel-air mixture
• Holes serve as air bleeds
How Carburetors Work – Load System
• As throttle plate opens
manifold vacuum causes
air flow across nozzle in
– Creates pressure difference
between fuel in bowl and
nozzle tip
– Atomized fuel flows out of
nozzle, mixes with air
• Amount of fuel controlled
by load needle
– Close too far, engine misses
– Open too far, fuel rises, extra
flows out holes in nozzle,
black smoke
How Carburetors Work – Economizer System
• Carb design problem
– Too rich at part throttle
• Load system operating
– Lean out mixture
• Air enters passage with
outlets to fuel bowl and
near throttle plate
– Hole near plate holds
economizer plug
• Throttle plate exposes hole
to vacuum, reduces
pressure on fuel bowl
– Reduces fuel flow from
Air Intake Passages – DLT Carburetors
Idle Air Intake
Accelerating Well
Air Intake
Bowl Vent Air Intake
Looking in Choke End of DLTX51
How Carburetors Work – Starting Engine
• Starting a tractor
– Open gas supply to carburetor
• Fuel flows into bowl, past load needle into nozzle, and thru
nozzle holes into accelerating well
– Close choke
– Advance throttle lever half way (Owner’s Manual)
• Fully open throttle plate
• Closed choke plate
– Full manifold vacuum applied to nozzle tip
– Turn flywheel to create manifold vacuum
• Difference between pressure on fuel in bowl and nozzle tip
causes fuel to flow from nozzle and acceleration well
– Tractor starts
– FSB 200 recommends nearly closed throttle plate
How Carburetors Work - Idling
• Slow idle (throttle lever pulled back)
– Throttle plate nearly closed
• Only primary idle hole open to manifold vacuum
• Secondary hole adding air
• Fast idle (throttle lever wide open)
– Throttle plate open to expose both primary and
secondary idle holes to manifold vacuum
– Fuel flows from both idle holes
• Maximum flow of fuel in idle circuit
• Amount of fuel allowed into idle circuit controlled
by idle needle
• Insufficient air flow past throttle plate for venturi
How Carburetors Work - Idling
• Setting idle needle for slow idle
– Pull throttle lever back to slow idle stop
• DLTX67-73 carbs, engine will stop
– Throttle plate hides both idle holes from manifold vacuum
– Do not pull lever back to stop to set idle
– Want only primary idle hole exposed to vacuum
• Air for idle circuit enters at venturi on right side
• Fuel enters at idle needle seat to create fuel-air mixture
– Idle circuit MUST be clean and to size
• Fuel-air mixture exits primary hole to manifold vacuum
– Secondary hole provides additional air
– Start with idle needle open ~1 turn, open 1 notch…..
• Wait for 15 sec, open, … repeat
• No unmetered sources of air
– If settings don’t work for middle or fast idle, check idle
hole sizes
– Lean a setting as possible to reduce plug fouling
How Carburetors Work – Sudden Load Applied
• Carburetor goes from idle to load circuits
– At idle, acceleration well full
– When load suddenly applied, extra fuel needed
• Governor opens throttle plate quickly
– Full manifold vacuum applied
• Venturi action starts pushing fuel from bowl thru nozzle
• Additional fuel flows through nozzle holes
– Provides rich mixture for short time until well empties
– If load remains
• Nozzle holes act as air bleeds, air comes from well vent
• Provides proper fuel-air mixture for load
– If load goes away
• Back to idle circuit operation, accelerating well refills
How Carburetors Work – Under Load
• Throttle plate opening set by throttle lever
and governor
• Manifold vacuum and venturi effect causes
fuel to flow from nozzle
– Amount depends on desired engine speed
• If lever set mid-range, economizer circuit leans out
the fuel-air mixture
• If lever set wide open, throttle plate open past
economizer plug opening, venturi action overcomes
economizer action, increases fuel in mixture
• If lever wide open and rated load applied, throttle
plate wide open, venturi action and fuel-air ratio
How Carburetors Work – Under Load
• Setting load needle – done under load
– Apply rated load to engine
– Close load needle until engine sputters
• Fuel flow thru needle less than flow thru nozzle
– When fuel level drops below nozzle bottom, draws air
– Open load needle until black smoke
• Fuel flow thru needle greater than flow thru nozzle
– Fuel flows up into acceleration well and out nozzle holes
» Fuel-air mixture too rich for engine to burn
– Set load needle ~ half-way between close and
open positions
Discussion of particular carburetors
• Early Wheeler Schebler carburetors on
Waterloo Boy and D
• Brass and cast iron carburetors
• General DLT series carburetors
• DLTX67-73
• Universal DLT replacement carburetors
Wheeler Schebler Model D Carburetor
Choke unit
Wheeler Schebler Model D Carburetor
• Original Schebler design – sold since 1904
• Air-valve design
– No venturi
Air Valve
Wheeler Schebler Model D Carburetor
• Carburetor not very sophisticated
No idle circuit
No venturi
Has bowl vent
Setting of air valve seems important
• Operation
– As throttle plate opens, manifold vacuum is applied,
action similar to having choke on
– Atmospheric pressure acts on fuel in bowl
– Low pressure across nozzle tip causes fuel to flow,
needle valve sets amount of fuel
• Loosen air valve – more air allowed in, less pressure
difference – less fuel – engine slows down
• Turn air valve in – spring holds valve tighter – less air in,
more pressure difference, more fuel, engine speeds up
Wheeler Schebler Model D Carburetor
• Combination of needle valve setting and
air valve spring tension very important
• Air valve setting normally 1/2” to 5/8” from
• Condition of spring important for correct
pressure on valve
• There are good-running Waterloo Boys
and spoker D’s, so apparently it can be
Early Wheeler Schebler Carburetors
• Waterloo Boy used Schebler D
– No choke device listed in parts books
– No throttle shaft bushings
• Model D also used Schebler D
– AD-28
• 30401-30450
• Different part numbers than DX298 or DX304
– AD-107
• 30451 – 31304
– DX298 (used in Nebraska Test 102 on 30504)
• 31305 - 49773
– DX304
Wheeler Schebler DLTX1
• Used on 605 D’s between 39907 and 46767
– AD107 DX304 Schebler D was “usual” carburetor
– AD287 DLTX1 was “trial”
• Air intake end has no flange
– AD411 DLTX3 followed DX304, started at 49774
Wheeler Schebler DLTX3
• Model D from 49774 – 109943 (mid ’27 – ’30)
– Replaced by DLTX6 at 109944 (Nov 1930)
Linkert brass float (H-D motorcycle) works
Bowl vent not in air passage
Most parts available
Only 1 idle hole outlet
Bowl Vent hole
(Load Needle)
Brass vs Cast Iron Carburetor Bodies
• Brass (actually bronze) carburetors were
used on the A, AR series, D, and GP series
• DLTXa (brass) went to DLTXa+10 (cast iron)
• First B Oct-2-34 used cast iron carb
• Change from brass to cast iron
– A – early December 1935
– AR-AO-AI – mid April 1936 DLTX9 to DLTX19
– D – late April 1936
– GP is confusing (as usual!!)
• Appears all Schebler carburetors were brass from the
– DLTX5 for GP, GPO, GPWT, and DLTX7 for OTS GPWT
General DLT series carburetors
• All same size, so will interchange physically
– Terrible idea, though!
• Don’t swap D carb with carb for other model
– Governor rod on opposite side of pivot
• Governor tries to slow down – but speeds up.. baad
• Some parts critical to operation are different
Throttle and choke plates
Economizer plugs
Internal passage sizes
• Primary and secondary idle holes
• Make sure all internal passages are clean
General DLT Series Carburetor Issues
• Eliminate sources of unmetered air
– Fit bushings to interior shape
– Seal threads on brass plugs and needles
– Make flanges flat (machine or sand)
• Set float for proper fuel level
– Use hose barb and clear tubing in bowl drain
– 3/4” down from bowl gasket for all carbs with
metal floats, EXCEPT
– 5/8” for DLTX67-73 carbs
• Clean strainer under screen – rusty
• Use pliable gaskets, not hard ones
General DLT Series Carburetor Issues
• Check surface where seat sets
– Often pitted – resurface smooth
• DLTX67-73 (late A and B)
– Two brass bowl vent plugs in vent hole
• Make it hard to tell if vent hole is open
– If plugged, cause all sorts of problems
• Carb operation depends heavily on correct
pressure on fuel in bowl
– Spring-loaded off-center choke
• Partially opens when tractor starts
Duplex Carburetors
• Operation
• Service hints
• Similar to single barrel carburetors
Duplex Fuel Control System
• Fuel enters inlet, into
– Traps dirt, drain to clean
• When sump full, flows
through screen,
needle, seat
• Proper fuel level at top
of bowl/gasket
• Holding carb upside
down, “top” of float
should be 3/4” from
bowl gasket surface
Duplex Bowl Air Vent System
• Large Pitot tubes and
passage vent fuel in
bowl to atmosphere
• Blockage unlikely
– Better than 1 barrel
• Pitot tubes also play
role in choke and
economizer systems
• All air passes through
air filtering system
Duplex Idle System – Slow Idle – 1 barrel
• 2 or 3 idle holes (2 in
– When throttle closed
• One on manifold side
• 1-2 on venturi side
• Manifold vacuum on 1st
Hole pulls air from Air
Bleed hole and fuel from
bottom of neck
• 2nd and 3rd idle holes
add more air to lean out
• Idle needle controls
mixture, not fuel alone
Duplex Carburetor Idle and Load Fuel Feeds
Idle fuel feed holes
Load jets (removed)
Duplex Idle Air Feeds and Nozzle Well Vents
Pitot Tubes
Idle Air Feed
Nozzle Well Vent
Holes toward center are Nozzle Well Vent holes
Holes toward outside are Idle Air Feed holes
Duplex Idle System – Fast Idle – 1 barrel
• 2nd and (then 3rd) idle
holes exposed to
manifold vacuum as
throttle plate opens
– Feed air-fuel mixture
– Graduated system for
smooth operation
• Merges into load
operation smoothly as
throttle plate opens
and venturi actions
Duplex Accelerating System
• During idle, no nozzle flow,
accelerating well fills to fuel
level in bowl
• When throttle plate opened
fast, lots of fuel needed
– Full venturi vacuum so
maximum ∆P between nozzle
top and bowl fuel
– In addition, fuel flows from
accelerating well thru nozzle
• Engine speed increases,
air flows from air bleed hole
through nozzle holes to
lean mixture out at steady
state speed
Duplex Load System
• Engine speed set by
governor/speed lever
• Increase load, throttle
plate opens, more ∆P,
more fuel from nozzle
• Fixed load jets
– Sized to carb and fuel
– Limit fuel flow
• Metering screw
Center of bowl nut
Adds additional fuel
2 ¼ turns open
Lots of service issues
Duplex Economizer System
• Simpler than 1 barrel system
– No economizer plug near throttle plate
• Carburetor designed for proper mixture at light
load operation
– Too lean for full load
– Additional fuel must be supplied
• As throttle plates open under load
– More air drawn, moves faster to manifold vacuum
– Part of air “rammed” thru Pitot tubes, adding pressure
to fuel in bowl
• Increased ∆P, more fuel flows as more air flows
• Decrease load, less air flow, less “ramming”
Duplex Choke System
• Similar to 1 barrel carb
• Choke disks close air flow
thru barrels
– Flow thru Pitot tubes not
• Maximum manifold vacuum
on nozzle tops
• 14 psi pressure on fuel in
bowl thru Pitot tubes
– Max ∆P, lots of fuel flow from
nozzle and idle holes
• Not much air flow
• Choke plates spring-loaded
and offset
– Engine starts, air flow pushes
disks open
Duplex Repair Information
• Remove metering screw from center of bowl nut
– Unscrew until loose, may have to pull
– Inspect end – should have tapered ss piece held on
by small spring washer
– Inspect metering screw seat
• Has slots for fuel flow, NOT unscrewing
• No reason to remove
• Remove bowl, inspect
– Often bent, bottom bowed in
• Press straight
• Reproductions available
• Disassemble carburetor
– Remove nozzles, throttle and choke plates, etc.
Duplex Fuel Metering Screw
Spring Washer
Duplex Repair Information
Remove load jets
Remove idle needles
Identify holes where fuel enters idle circuit
Remove small freeze plugs just above bowl on
each side of carb
– Carefully drill, tap for 10-32 screw, pull
• Can reuse, filling holes with JBWeld, or use new plugs
– See two holes
– Good intermediate place to access idle circuit
– Spray carb cleaner into idle pickup hole in neck
• Should come out hole
– Spray cleaner into hole toward idle needle
• Should come out idle holes
Duplex Carburetor Freeze Plug Removed
To Idle holes near throttle plate
From Idle Air Inlet
Idle Needle (removed)
From Idle Fuel Inlet below nozzle
Duplex Repair Information
• If carb cleaner does not come thru holes
have blocked passages
– Probably need to remove ball bearings
• Not brass plugs like in 1 bbl
• Hard – Rockwell Hardness Rc48 at least
– Wire weld tail on ball, pull with slide hammer
• May have to drill hole to top of ball to access
• Clean passages (once open)
– Replace balls (or drill and tap for brass plugs)
• Clean nozzles
• Inspect throttle shaft, bushings for wear
Duplex Repair Information
• Check float
– Place in boiling water, look for bubbles
• If see bubbles, bad float
• Check needle and seat
– Pull vacuum see if hold
• Clean body, do any necessary repairs
• Reassemble, set float level 3/4”
• Use new, soft gaskets
– Bowl gasket goes under bowl, not under bowl nut
• Can use hard gasket under nut
• Leak check, check fuel level (at bowl gasket)
Marvel Schebler Universal Carburetors
• Between 1969 and 1974 all single and duplex
carburetors were collapsed into three units
• DLTX107U replaced DLTX5, 8, 10, 15, 17, 18,
19, 26, 34, 46, 67, 73
• DLTX108U replaced DLTX3, 6, 16, 24, 33, 41,
51, 53, 63, 71, 72
• DLTX109U replaced all duplex units
• Identified by circular aluminum tab with number
stamped on it, brass drill plugs riveted in, not
• Discontinued in 1983 when M-S plant closed
TSX Series Carburetors
• Theory
• Repair
• Used on Wagon Works and Dubuque
series tractors
– L, LA, LI, M, etc.
– 62 and Unstyled L used TCX series (similar)
• Problem
– Parts books list bowl separately but top
includes throttle shaft and plate
• Hard to compare to see if tops can interchange
TSX Basic Principles – Updraft Carburetor
• Similar concept to DLT
• Air enters, passes thru
venturi where its velocity
increases and pressure
decreases, then back to
low velocity and
• Nozzle tip located in
venturi at point of low
pressure so fuel flows
out nozzle
• Bowl vent connects to air
inlet, as on DLT
TSX Fuel and Choke Systems
• Fuel enters thru strainer
– Fastened on end of inlet
• Flows thru needle and seat
– Fuel level 5/8” below bowl
• Close choke to start
– Extends manifold vacuum
past nozzle
– Bowl vent takes air from left
side of choke
• Large ∆P between nozzle tip
and fuel in bowl
– Rich fuel-air mixture
• Engine starts – choke off
center or has flap so air
TSX Load System
• Some carbs have load
needle, some have fixed
load jet only
• Throttle plate position set
by governor/speed control
– Governor maintains speed
• More load, throttle opens more
• When maximum load
applied, throttle plate fully
open, maximum fuel-air
mixture flows to engine
TSX Accelerating System
• At idle, fuel flows thru
load system into
nozzle, out nozzle
holes into
accelerating well, to
bowl fuel height
• Throttle opened
rapidly, fuel flows out
of nozzle tip, and out
of well thru nozzle
• When empty, air flows
thru vent and nozzle
holes – leans mixture
Accelerating Well Vent
TSX Idle System
• Slow idle
– Manifold vacuum applied to
primary (top) idle hole
• Large ∆P between fuel in bowl
and primary hole
– Fuel forced from acceleration
well thru idle passage
– Fuel mixes with air at idle
needle seat
• Additional air from secondary
– Proper air-fuel mixture flows
from primary hole
• Fast idle – both primary and
secondary holes flow
• NOTE: Idle Needle controls
AIR, NOT fuel
Idle Air inlet
TSX Economizer System
• Similar to DLT
• Bowl vent air enters
around venturi
Economizer jet
• As throttle plate nears
economizer hole,
manifold vacuum
applied to red
economizer passage
Economizer hole
– Economizer jet limits
air flow
– Lowers pressure on
fuel – less fuel thru
• All carbs with load
needle have econ jet
– Some carbs without
load needle have jet
Bowl Vent air
TSX Economizer System
• Similar to DLTX
• Bowl vent air enters
around venturi
Economizer jet
• As throttle plate nears
economizer hole,
manifold vacuum
applied to red
economizer passage
Economizer hole
– Economizer jet limits
air flow
– lowers pressure on
fuel – less fuel thru
• All carbs with load
needle have econ jet
– Some carbs without
load needle have jet
Bowl Vent air
TSX Service Information
• Separate top from bowl – 4 screws
• Remove gasket, venturi
• Word on jets
– Grind screwdriver to fit “perfectly”
– Be gentle in attempts to remove
• If stuck and force, spread out edges which dig into casting –
making it harder to remove
• Apply heat, let cool
• Sometimes have to drill out
• For top
– Remove float, check
– Remove idle jet (at angle)
– Check for economizer jet – deep in hole
• If present, remove
TSX Service Information
• Top service, cont’d
Remove idle needle
Remove needle and seat
Remove throttle plate (note how located)
Check throttle shaft for looseness
• Wear on shaft – replace
• Wear in shaft holes – usually no bushings
– Machine for bushings – can be tricky
– Clean all passages (idle, economizer, vent)
– Assemble with new gaskets, necessary parts
– Set float ~level with top upside down
• Bowl service
– Remove choke plate (note how located)
• Remove choke shaft, note how spring wound
TSX Service Information
• Bowl service cont’d
– Remove load needle if present
– Remove bowl drain
– Remove nozzle
Some unscrew from venturi area
Some unscrew from bottom after remove needle
Again, use proper screwdriver and/or heat
Remove gasket on end of needle
– May be stuck in recess
– Clean all passages
– Reassemble with new gaskets
• Assemble top to bowl
• Check fuel level – 5/8” from top gasket
Zenith TU Carburetors – Diesel Starting Engines
• Used first on 70D (Oct 1954)
– R used Marvel Schebler SL-2 mixer
• Information available is inconsistent
– Zenith catalogs and specification sheets
• O-11681 (AF2414R) used from 1954-57
• O-12028 (AF2146R) was “service replacement”
• O-12172 (AF3775R) used from 1957-1960
– Deere parts catalogs, MPI, …
• AF2414R doesn’t exist
• AF2146R used on 70D and 720D to 7214899
– Also on 80, 820 to 8203099
• AF3775R used from 7214900 to end, and all 730
– Also on 820 8203100- end, and all 830
Zenith TU Carburetors – Diesel Starting Engines
• AF3775R was replacement for others
• 70D carburetor used “deflecting ring”
between throttle plate and manifold
– Changed manifolds at 7034100
• Removed deflecting ring
• Gone from then on
• All versions take K2067 kit
– Gaskets, needle and seat
– Anything more will be expensive
History of carburetor companies
Carburetor types
Carburetor systems and how function
Operation and servicing of popular units
Handout available
Handouts from the Gathering of the Green
workshops are among the information included
on the CD available through this web site.

Similar documents