tillotson hs series carburetors
Contents
1. oe 9 8 4 4 OPERATIONAL DATA OPERATIONAL DATA _ ATMOSPHERIC AIR __ PUMP IMPULSE AIR SUPPLY FUEL FUEL UNDER PRESSURE FUEL UNDER VACUUM FUEL INLET CONTROL LEVER MAIN FUEL DISCHARGE PORT CHOKE SHUTTER INLET TENSION SPRING e Seen ER Sis Spey hy e d poani Se eee oa sec etme Joa THROT TLE SHUTTER SECONDARY IDLE FUEL DISCHARGE PORT PRIMARY IDLE FUEL DISCHARGE PORT MAIN DIAPHRAGM FUEL CHAMBER wes 7 eT E MAIN DIAPHRAGM STARTING CHOKE OPERATION 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 INLET NEEDLE FUEL INLET CONTROL LEVER EENEN AA ts 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 supply2. gt pump Ruptured fuel pump diaphragm gt Main fuel orifice plugged The 7 32 diameter nozzle welch gt plug or nozzle check valve cage is not sealing REMEDY 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 INMAKING CARBURETOR ADJUSTMENTS TURN ADJUSTMENTS CAREFULLY AND GENTLY DO NOT RAM ADJUSTMENTS INTO SEATS Set engine idling speed in accordance with engine manufacturer s recommendation 7i TROUBLE DATA Continued Be sure all Cover Screws are tight to insure perfect seal COVER SCREW Fuel Pump Dia phragm must be free of breaks PUMP DIAPHRAGM and punctures SPRING IDLE MIXTURE SCREW 6 32 THD HIGH SPEED MIXTURE SCREW 8 32 THD IDLE SPEED SCREW SPR
3. orifices and channels and out the discharge ports to the engine THROTTLE SHUT TER PRIMARY IDLE FUEL DISCHARGE PORT IDLE ADJUSTMENT SCREW ORIFICE MAIN DIAPHRAGM FUEL CHAMBER lt SSS NNN EG INLET TENSION SPRING MAIN DIAPHRAGM IDLING OPERATION 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 VENTURI A V MAIN FUEL DISCHARGE PORT re MAIN ADJUSTMENT SCREW ORIFICE SSS OE SHUTTER ERINI THROTTLE SECONDARY IDLE FUEL DISCHARGE PORT MAIN DIAPHRAGM FUEL CHAMBER INTERMEDIATE OPERATION 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 t
4. Dotson TILLOTSON LTD CLASH INDUSTRIAL ESTATE TRALEE CO KERRY IRELAND PHONE 353 66 7121911 FAX 353 66 7124503 e mail sales tillotson ie HS SERVICE MANUAL INTRODUCTION 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 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 CONSTRUCTION DATA AND CHART fi SANANA BN ENA A A A Lee 29 28 27 ea J DVG 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 DAOOODS ia ae Segal 3 15 25 1 20 19 18 7 16 HS SCHEMATIC Filtering Screen Venturi Pulse Chamber Fuel Chamber Fuel Pump Diaphragm Diaphragm Pump Inlet Valve Diaphragm Pump Outlet Valve Fuel Pump Body Fuel Pump Gas
5. ING WELCH PLUG If necessary to clean remove Welch Plug and blow with com pressed air NOZZLE SCREEN RETAINING RING WELCH PLUG Main Diaphragm must be free of breaks or punc tures ONTROL SPRING CONTROL LEVER sag D M COVER PUMP GASKET PUMP DIAPHRAGM SPRING CHOKE O ERICTION BALL INLET NEEDLE FULCRUM PIN PIN RETAINING SCREW DIAPHRAGM GASKET DIAPHRAGM DIAPHRAGM COVER COVER SCREW Pump Gasket and Pump Diaphragm must locate on cast pins on Pump Cover If necessary re move and clean Strainer Screen with compressed air Do not stretch or distort Control Spring Control Lever must rotate freely on Fulcrum Pin Set Control Lever flush with floor of metering chamber Locate Diaphragm Gasket Main Diaphragm and Cover on cast pins in Body
6. SCREW Your HS Carburetor may have this style of Metering Diaphragm METERING INLET CONTROL LEVER CHAMBER SET FLUSH WITH FLOOR CHAMBER FLOOR US SSE See SES an N a za win Wo 2 ae mE IDLE HIGH SPE VIATURE MIXTURE REW SCREW 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 THEN PUSH NEEDLE HERE DEPRESS HERE PRY UP HERE LOW 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 C Drill a 1 8 diameter hole through the 11 32 diameter welch plug This hole should just break
7. hrough the VENTURI A MAIN FUEL DISCHARGE PORT il MAIN ADJUSTMENT SCREW ORIFICE f AE e 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 fp S TS 55 SSN Nie Gp THROTTLE SHUTTER MAIN DIAPHRAGM HIGH SPEED OPERATION 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 SERVICE DATA 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 METERING INLET CONTROL LEVER CHAMBER SET FLUSH WITH FLOOR An eeraa CHAMBER FLOOR IDLE HIGH SPEED MIXTURE MIXTURE SCREW
8. ket Fuel Inlet Impulse Channel Throttle Shutter Primary Idle Discharge Port Secondary Idle Discharge Port High Speed Mix Screw Orifice Idle Mixture Screw Body Metering Chamber Idle Mixture Screw Orifice Diaphragm Atmospheric Chamber Atmospheric Vent Diaphragm Cover Inlet Tension spring Fulcrum Pin Diaphragm Gasket Inlet Control Lever Inlet Needle High Speed Mixture Screw Choke Shutter Fuel Inlet Supply Channel Main Nozzle Discharge Port oe ele eee 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 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 i
9. nto 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 ADJUSTMENT INSTRUCTIONS Open high speed mixture screw one and one quarter 11 4 turns Open idle mixture screw one 1 turn SERVICE DATA HOW TO DISASSEMBLE FOR CLEANING AND REPAIR 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 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
10. 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 TROUBLE CARBURETOR FLOODS ENGINE WILL NOT ACCELERATE ENGINE RUNS OUT LEAN CARBURETOR RUNS RICH WITH HIGH SPEED MIXTURE SCREW SHUT OFF TROUBLE DATA PROBLEM Dirt or foreign particles preventing gt inlet needle from seating Diaphragm lever spring not seated on lever dimple Diaphragm improperly installed in gt carburetor Idle mixture too lean Incorrect setting on diaphragm lever Diaphragm cover plate loose gt i wa Diaphragm gasket leaking Main fuel orifice plugged Incorrect idle adjustment gt Idle discharge ports or channels 9 clogged Diaphragm lever set incorrectly Throttle shutter cocked in the throttle bore causing fast idle Dirty nozzle check valve or outlet gt 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 1
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