SERIES - Tillotson
Contents
1. SPRING p UMP COVER IDLE SPEED REG SCREW PUMP GASKET Fuel Pump Dia O phragm must be w PUMP D PUMP free of breaks AERRAGM gt DIAPHRAGM and punctures 7 INLET SCREEN FLANGE A GASKET SCREW SHUTTER 4 Da SCREW SHAFT CLIP THROTTLE SAUTTER RETURN SPRING THROTTLE SHAFT SCREEN Fae _ 7 RING IDLE ADJUSTMENT PE A DUUSTMEN NG conta CONTROL SPRING MAIN ADJUSTMENT SCREW ee ww FULCRUM PIN WELCH PLUG 4 jia iie hi Main Diaphragm E56 DIAPHRAGM must be free of J pi apHRAGM NS GASKET breaks or punc tures DIAPHRAGM DIAPHRAGM COVER pe COVER SCREW COVER g SCREW Be sure all Cover Screws are tight to insure perfect seal Pump Gasket and Pump Dia phragm must lo cate on cast pins on Pump Cover If necessary re move and clean Nozzle Screen with compressed air If necessary to clean remove Welch Plug and blow with com pressed air Do not stretch or distort Con trol Spring Control Lever must rotate freely on Fulcrum Pin Set Control Lever flush with floor ofmetering chamber Locate Dia phragm Gasket Main Diaphragm and Cover on cast pins in Body2. Bien a yayaon ID e NAN DS ONO WON FON TN INCE T NEEDLE N A Sa Sd zat an aS ONES r l bss FUEL INCET CONTROL LEVER 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 gany omg fh aN anans NN THROTTLE VENTURI SHUT TER MAIN FUEL DISCHARGE PORT SECONDARY IDLE FUEL DISCHARGE PORT e SE TAE ll MAIN ADJUSTMENT SCREW ORIFICE 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 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 a
3. 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 throttle idle and high speed mixture screws idle soeed screw and inlet needle High speed and idle 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 inlet needle on some models and a self tapping screw holds the fulcrum pin in place Movement of the pump diaphragm is caused by pulsations from the engine 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 pu
4. e 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 ADJUSTMENT INSTRUCTIONS OPEN HIGH SPEED MIXTURE SCREW AND IDLE MIXTURE SCREW ONE 1 TURN 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 INLET METERING CONTROL LEVER CHAMBER SET FLUSH WITH FLOOR CHAMBER FLOOR WHA OH UO ng IDLE HIGH SPEED MIXTURE MIXTURE SCREW 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 mod
5. els the inlet control lever is hooked to the inlet needle at one end Special care is required when reassembling these parts to insure proper operation DEPRESS THEN PUSH HERE NEEDLE HERE 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 1 Drill a 1 8 diameter hole through the 9 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 2 Carefully pry out the welch plug and clean discharge ports and cross channels To re install place welch plug in well convex side up and flatten with a flat end tool slightly larger than the welch plug 3 A nozzle brass cup plug can be removed in the same manner by using a 5 32 drill or if you have a check ball cage this should be pressed out and a new one pressed in _ hk oe ID TROUBLE SHOOTING Carburetor Floods Dirt or foreign particles preventing inlet needle from seating Diaphragm lever spring not seated on lever dimple Diaphragm improperly installed in carburetor Engine Will Not Accelerate Idle mixture too lean Incorrect setting on diaphragm lever Diaphragm cover plate loose Diaphragm gasket leaking Main fuel orifice plugged Engine Will Not Idle Incorrect idle adjustm
6. ent 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 screw shut off Engine Runs Out Lean Tank vent not operating correctly Leak in fuel system from tank to pump Ruptured fuel pump diaphragm Main fuel orifice plugged Carburetor Runs Rich with High Speed Mixture Screw Shut Off The 3 6 diameter nozzle cup plug 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 Set engine idling speed in accordance with engine manufacturer s recommendation TROUBLE SHOOTING
7. mp cover and diaphragm CHOKE SHUTTER THROTTLE SHUTIERK SECONDARY IDLE FUEL DISCHARGE MAIN FUEL PORT DISCHARGE PORT PRIMARY IDLE INCET NEEDLE Lo ie FUEL DISCHARGE ll PORT FUEL INLET ESQ m MAIN DIAPHRAGM CONTROL LEVER A a FUEL CHAMBER SQ n NE 020 ANOS WOOGONEE BX CH ONO HON AO Ege INLET TENSION SPRING MAIN DIAPHRAGM STARTING CHOKE OPERATION Starting an engine with the HU Carburetor involves the same methods that are used in a conventional float feed carburetor When starting a cold engine place the shutter blade 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 Atmospheric 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 Ze SEER ER Hs SSS E zah THROTTLE IDLE ADJUSTMENT SHUTTER SCREW ORIFICE PRIMARY IDLE oh a FUEL Decane r oo fa MAIN DIAPHRAGM FT FUEL CHAMBER Se
8. nd diminishes the suction on engine side of the throttle shutter When the pressure at the venturi throat is less than existing within main diaphragm fuel chamber fuel is drawn up through high speed mixture orifice and out main fuel discharge port into air stream entering engine intake THROTTLE VENTURI SHUTTER MAIN FUEL DISCHARGE PORT MAIN ADJUSTMENT FAQS S MAIN DIAPHRAGM SCREW ORIFICE 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 SUPPLY FUEL ATMOSPHERIC AIR FUEL UNDER PRESSURE PUMP IMPULSE AIR E FUEL UNDER vacuum HOW TO DISASSEMBLE FOR CLEANING AND REPAIR Before disassembling carburetor it is imperative to flush 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 Remove filtering screen 4 Remove main diaphragm cover screws and cover 5 Remove main diaphragm and gasket 6 Remove fulcrum pin screw pin control lever and spring 7 Remove inlet needle 8 Remov
9. o Mforsom TILLOTSON LTD CLASH INDUSTRIAL ESTATE TRALEE CO KERRY IRELAND PHONE 353 66 7121911 FAX 353 66 7124503 e mail sales tillotson ie MU SERVICE MANUAL INTRODUCTION To keep apace of new market demands Tillotson has designed and developed a new miniature all position diaphragm carburetor the HU series This versatile unit is lightweight and compact only a 1 1 8 cube but it still comprises a self contained fuel pump and filtering screen HU SCHEMATIC B A ES MPS at SF A 4 Nj oe DD DDC SS lt ae AK eass AF tsa m N lt os exe J wrrr Le f amp 5 8 iA 3839 j paa RA z See T n l OONOUOATUNRWD WwW gt Filtering Screen Venturi Fuel Chamber Pulse Chamber Fuel Pump Diaphragm Pump Diaphragm Inlet Valve Pump Diaphragm Outlet Valve Fuel Pump Body Fuel Pump Gasket Fuel Inlet Impulse Channel Throttle Shutter Primary Idle Discharge Port Secondary Idle Discharge Port Body Idle Fuel Adjustment Metering Chamber Idle Fuel Adjustment Orifice Diaphragm Cover Metering Diaphragm Atmospheric Chamber Atmospheric Vent Main Fuel Adjustment Orifice Inlet Tension Spring Fulcrum Pin Diaphragm Gasket Inlet Control Lever Main Fuel Adjustment Inlet Needle Main Nozzle Discharge Port Fuel Inlet Supply Channel CONSTRUCTION DATA The HU series
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