TILLOTSON HS Series User manual

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SERVICE MANUAL
TILLOTSON LTD., CLASH INDUSTRIAL ESTATE,
TRALEE, CO. KERRY, IRELAND
PHONE: [phone] FAX: [phone]
e-mail: [e-mail]

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The demand for a miniature all position diaphragm
carburetor prompted Tillotson to design and develop
the “HS” series. This small compact unit, only a 1-1/2
inch cube, is versatile in application because of its
lightweight and compact size. Even though the
carburetor is extremely minute, it still comprises a
self-contained fuel pump and filtering screen.
The “HS” series carburetor is die-cast aluminium,
consisting of three basic parts: metering body, pump
cover plate and main diaphragm cover plate. This
carburetor incorporates many of the components
found in float type carburetors: choke, throttle, idle
and high speed mixture screw and inlet needle.
Information contained in the following pages is
presented as an aid to understanding construction,
operation and servicing of the “HS” series carburetor.
Complete carburetors, repair kits and service parts
are available through our dealers.
Idle and high speed mixture screws are spring friction
type and require no packing. These mixture screws
are located on the right side looking toward air horn.
A rubber tipped needle seats directly on a machined
orifice in the body casting. An inlet tension spring
CONSTRUCTION DATA AND CHART
HS SCHEMATIC
1. Filtering Screen
2. Venturi
3. Pulse Chamber
4. Fuel Chamber
5. Fuel Pump Diaphragm
5A. Diaphragm Pump Inlet Valve
5B. Diaphragm Pump Outlet Valve
6. Fuel Pump Body
7. Fuel Pump Gasket
8. Fuel Inlet
9. Impulse Channel
10. Throttle Shutter
11A Primary Idle Discharge Port
11B Secondary Idle Discharge Port
12. High Speed Mix. Screw Orifice
13. Idle Mixture Screw
14. Body
15. Metering Chamber
16. Idle Mixture Screw Orifice
17. Diaphragm
18. Atmospheric Chamber
19. Atmospheric Vent
20. Diaphragm Cover
21. Inlet Tension spring
22. Fulcrum Pin
23. Diaphragm Gasket
24. Inlet Control Lever
25. Inlet Needle
26. High Speed Mixture Screw
27. Choke Shutter
28. Fuel Inlet Supply Channel
29. Main Nozzle Discharge Port
INTRODUCTION

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exerts a pre-determined force on the inlet control
lever, which holds the needle on its seat.
A metering diaphragm is subjected to engine suction
on the metering chamber side and atmospheric
pressure on the vented side. Atmospheric pressure
on the vented side pushes the diaphragm toward the
inlet control lever opening the inlet needle to allow
fuel to enter the metering chamber, from which it is
then delivered into the mixing passages.
The inlet control lever hooks on the center of the
metering diaphragm and a self tapping screw holds
the fulcrum pin place.
Movement of the pump diaphragm is caused by
pulsation’s from the engines, acting on it through an
impulse channel. This movement draws fuel into the
fuel chamber and a reverse movement forces fuel out
of the fuel chamber through the inlet needle into the
metering chamber.
An easily accessible fine mesh-filtering screen is
located under the fuel pump cover and diaphragm.
Before disassembling carburetor it is imperative to
blush it clean of sawdust and dirt by pouring gasoline
over it and tools.
1. Remove pump diaphragm cover screws and
cover.
2. Remove pump gasket and pump diaphragm.
3. Remote filtering screen.
4. Remove main diaphragm cover screws and
cover.
5. Remove main diaphragm and gasket (slide
diaphragm towards mixture screws approximately
1/16
th
of an inch and pull up to unhook from the
control lever).
6. Remove fulcrum pin screw, pin, control lever and
spring….
7. Remove inlet needle.
8. Remove idle and high speed mixture screws and
springs.
Commercial carburetor cleaner can be used on all
parts except diaphragms and gaskets. Before
reassembling, rinse all parts in clean gasoline and
blow off with compressed air. Do not use cloth, as
tiny particles of lint adhering to carburetor parts will
cause malfunction. Channels in the metering body
can be cleaned by blowing through idle and high
speed mixture screw orifices. Do not use wires or
drills to clean orifices.
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ADJUSTMENT INSTRUCTIONS
Open high speed mixture screw one and one quarter (1¼) turns.
Open idle mixture screw one (1) turn.
SERVICE DATA
HOW TO DISASSEMBLE FOR CLEANING AND REPAIR

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Starting an engine with the “HS” Carburetor involves
the same methods used in a conventional float feed
carburetor.
When starting a cold engine, place the choke shutter
in the closed position and throttle shutter in a cracked
or open position. As the engine is cranked, engine
suction will be transmitted to the diaphragm fuel
chamber through both primary and secondary idle
discharge ports as well as the main fuel discharge
port, creating a low pressure area on the fuel side of
the main diaphragm. Atmosphere air pressure on the
opposite side will force the main diaphragm upward
causing the diaphragm button to depress the inlet
control lever, overcoming inlet tension spring
pressure, permitting fuel to enter through the inlet
seat, then into the fuel chamber side of main
diaphragm, up through the idle and high speed fuel
supply orifices and channels, and out the discharge
ports to the engine.
When engine is idling, throttle shutter is partially
cracked. Engine suction is transmitted through the
primary idle fuel discharge port to the fuel chamber
side of main diaphragm via the idle fuel supply
channel. Again, the main diaphragm is forced upward
by atmospheric pressure, depressing the inlet control
lever overcoming inlet tension spring pressure and
permitting fuel to enter through inlet seat, and filling
the fuel chamber. Fuel is then drawn up through idle
mixture screw orifice and delivered to the engine
through primary idle discharge port.
OPERATIONAL DATA
STARTING (CHOKE) OPERATION
IDLING OPERATION

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Fuel is delivered into and through the carburetor in
the same manner as when the engine is idling.
However, as the throttle opens and the engine speed
increases, more fuel is supplied to the engine by
valving in the secondary idle discharge port located
immediately behind the throttle shutter.
As the throttle shutter continues to open and engine
Speed increases, the velocity of air through the
venturi creates a low pressure area at the venturi
throat and diminishes the suction on engine side of
the throttle shutter. When the pressure at the venturi
throat is less than that existing within main diaphragm
fuel chamber, fuel is drawn up through high speed
mixture orifice and out main fuel discharge port into
the air stream entering engine intake.
As the throttle shutter progressively opens from
intermediate position to full open position, the air
velocity through the venturi increases and fuel is
metered up through high speed mixture orifice and
main fuel discharge port in accordance with the power
requirements of the engine. The action of the main
diaphragm is the same as previously described with
suction required to operate the diaphragm being
transmitted through the main fuel discharge port.
INTERMEDIATE OPERATION
HIGH SPEED OPERATION

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SERVICE HINTS
Be certain both diaphragms are installed correctly -
the
pump diaphragm next to the metering body, then the
gasket – the main diaphragm gasket, then the main
diaphragm. Evenly tighten all screws to insure
complete
seal.
When reassembling the inlet control lever and spring,
care should be taken to see that the spring rests in
the well of the metering body and locates on the
dimple of the inlet control lever (as illustrated above).
CAUTION: Do not stretch spring. Inlet control lever is
properly set when flush with the floor of the
diaphragm chamber. If diaphragm end of control
lever is low, pry up. If lever is high, depress
diaphragm end and push on needle for proper
adjustment. (See illustration). On some models the
inlet control lever is hooked to both the inlet needle at
one end and the metering diaphragm at the other. On
other models the inlet lever is hooked to the inlet
needle while the opposite end of the lever merely
rests against the metering diaphragm. Special care is
required when reassembling these parts to insure
proper operation.
CAUTION:
Under extreme conditions of
clogged idle fuel channel and discharge ports, it may
be necessary to remove the channel welch plug. If
so, it must be done very carefully in the following
manner:
Drill a 1/8 “ diameter hole through the
11/32” diameter welch plug. This hole
should just break through the welch plug.
Deeper drilling will seriously damage the
body casting and render the carburetor
non-serviceable.
Carefully pry out the welch plug and
clean discharge ports and cross
channels. To reinstall, place welch
plug in well, convex side up, and flatten
with a flat end tool slightly larger than
the welch plug. Nozzle welch plug can
be removed in the same manner by
using a 1/16” drill.
SERVICE DATA
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CARBURETOR
FLOODS
ENGINE
WILL NOT
ACCELERATE
ENGINE WILL
NOT IDLE
ENGINE RUNS
OUT LEAN
CARBURETOR
RUNS RICH
WITH HIGH
SPEED MIXTURE
SCREW SHUT
OFF
Dirt or foreign particles preventing
inlet needle from seating.
Diaphragm lever spring not seated
on lever dimple
Diaphragm improperly installed in
carburetor
Idle mixture too lean.
Incorrect setting on diaphragm lever.
Diaphragm cover plate loose.
Diaphragm gasket leaking
Main fuel orifice plugged
Incorrect idle adjustment
Idle discharge ports or channels
clogged.
Diaphragm lever set incorrectly.
Throttle shutter cocked in the throttle
bore causing fast idle.
Dirty nozzle check valve or outlet
screen.
Welch plug covering the idle discharge
ports does not seal. This causes the
engine to idle with idle mixture shut off.
Tank vent not operating correctly.
Leak in fuel system from tank to
pump
Ruptured fuel pump diaphragm
Main fuel orifice plugged
The 7/32 “ diameter nozzle welch
plug, or nozzle check valve cage, is
not sealing.
Remove, clean and replace
Remove lever and reinstall
Replace diaphragm or correct
installation.
Readjust
Reset
Tighten
Replace
Remove diaphragm cover,
diaphragm, diaphragm lever and
high speed mixture screw. Clean out
orifice by blowing through high
speed mixture screw threaded hole.
Reset to best idle
Blow out with compressed air, or, if
compressed air is not available,
clean and flush with gasoline.
Reset diaphragm lever so it is flush
with the floor of the diaphragm
chamber.
Reset
Clean or replace.
Replace welch plug, following
instructions outlined in service hints.
Clean, if possible, or replace
Tighten or replace fittings or line
Replace
Clean
Install new plug or
new cage
Note: IN MAKING CARBURETOR ADJUSTMENTS TURN ADJUSTMENTS
CAREFULLY AND GENTLY – DO NOT RAM ADJUSTMENTS INTO SEATS.
Set engine idling speed in accordance with engine manufacturer’s recommendation.
TROUBLE DATA
TROUBLE PROBLEM REMEDY

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