HOMELITE CHAINSAW Repair Manual

CARBURETOR SERVICE CHAIN SAW CARBURETOR SERVICE GENERAL CARBURETOR SERVICE ENGINE OPERATIONAL SYMP- TOMS. Refer to Fig. TR1 for schematic view of typical diaphragm carburetor showing location of parts. Normally en- countered difficulties resulting from carburetor malfunction, along with possible causes of difficulty, are as follows: A. ENGINE WILL NOT START OR HARD TO START. Could be caused by: (1) incorrect idle mixture screw adjustment, (2) restricted or plugged fuel filter or fuel line, (3) throttle shaft worn, (4) choke shaft worn or not functioning properly, (5) inlet needle valve stuck closed, (6) metering lever worn, bent, binding, or set too low, (7) metering diaphragm cover vent hole restricted or plugged, (8) metering diaphragm, gasket or cover leaking, (9) low speed fuel passages restricted or plugged. B. GARB caused by: ( preventing i ing, (2) dam die and/or s ing of needle, not seated c (4) metering high, (5) hoi Welch plug Also, when carburetor, leaking fuel :ETOR FLOODS. Could be I) dirt or foreign particles |let fuel needle from seat- led or worn fuel inlet nee- it preventing proper seat- '3) diaphragm lever spring ;ly on diaphragm lever, |lever binding or set too in pump diaphragm, (6) fuel chamber is loose, icl tank is located above •ding can be caused by lump diaphragm. C. ENGIN1 caused by: (1] (2) restricted high speed fuj hole in fuel metering level or set too loi screw incorrei pulse passage, carburetor ai RUNS LEAN. Could be fuel tank vent plugged, [uel filter or fuel line, (3) 1 passages restricted, (4) .etering diaphragm, (5) worn, binding, distorted (6) high speed mixture ttly adjusted, (7) leak in |8) leaky gaskets between cylinder intake port. Also, check for leaking crankshaft seals, porous or cracked crankcase or other cause for air leak into crankcase. D. ENGINE WILL NOT ACCELER- ATE SMOOTHLY. Could be caused by: (1) idle or main fuel mixture screws set too lean on models without accelerating pump, (2) inoperative accelerating pump, on carburetor so equipped, due to plugged channel, leaking diaphragm, stuck piston, etc., (3) restricted low speed fuel passage, (4) restricted tank vent, fuel filter or fuel line, (5) plugged air filter, (6) restricted vent hole in metering cover, (7) restricted pulse channel, (8) defective pump diaphragm, (9) metering lever set too low, (10) defective manifold or carburetor mounting gaskets. E. ENGINE STOPS WHEN DE- CELERATING. Could be caused by: (1) ;o Flange gasket defective, engine, speeds up and idle is very lean and erratic Throttle shutter coclj fast idle ! causing Welch plug loose causing flooding Welch plug loose causing engine to run rich with main adj. closed Impulse channel plugged causing v inoperative fuel pump >^ Dirt in idle system causing erratic idle Dirt in removable metering jet causing lean operation & no power Dirt in main system causing, lean operation Inlet connection gasket not sealing causing lean operation Filter plug screw gasket leaking causing lean operation Plugged filter causing ,lean operation Dirt under inlet needle causing flooding Low lever setting causes lean operation and poor acceleration Lever binding on fulcrum pin causes flooding or lean operation High lever setting causes flooding or (ean operation > Body gaskets defective causing lean operation Body screws loose causing lean operation Hole in metering diaprj causing lean operatior Fig. TR1—Schematic cross-sectional view of a dlaphras agm Hole in pump diaphragm causing rich operation type carburetor Illustrating possible causes of malfunction. 12

SERVICE MANUAL SAW CHAIN tion in pitch which will contribute to rapid wear of sprocket teeth. 6. A badly worn bar will contribute to rapid wear of the chain which will cause the sprocket to wear. Rapid deterioration and wear on chain drive lugs, side links and cutters will result from installing a new chain. Never install a new chain on a worn sprocket or bar. CLUTCH CLUTCH BEARING. The clutch drum and sprocket can rotate freely (or stop) when the clutch is disengaged. A caged needle roller bearing is located between the clutch drum hub and the shaft. The bearing on most models uses the shaft as the inner race and the clutch drum hub as the outer race and can be removed by hand without any special tools. Clutch needle bearing failure is often caused by storing the saw after oper- ating under extremely wet conditions. The water will penetrate the needle bearing, form rust and cause the needles to become locked. It is recommended that the clutch drum be removed periodically (depending on local conditions) and the bearing repacked with a good grade of water-resistant grease (not water pump grease). CLUTCH DRUM AND SHOES. Rapid clutch drum wear, shoe glazing Fig. CM31—View of self-aligning sprocket (left) and worn integral star sprocket (right). Bar- RIM Chain— II lirrt Fig. CM32—View of typical self-aligning sprocket and clutch assembly. Note that sprocket can float on spllned hub to align with bar groove. or grooving may be caused by any of the following: 1. Improper filing. Hooked cutters and excessive joint will especially cause the clutch to slip. 2. Chain pinched in cut causing clutch to slip. Throttle should be released immediately when chain becomes pinched. 3. Oil soaked or worn clutch shoes. Clutch shoes should be inspected periodically. Glazing can be removed by wire brushing or other similar method. OFF-SEASON STORAGE When storing a chain saw for periods longer than 30 days, the following storage instructions should be followed: Drain all fuel from the fuel tank. Start and run the engine until it stops to remove fuel from carburetor. Drain oil from oil tank. Remove guide bar and chain and clean them thoroughly. Store the chain in a small container with engine oil covering the chain. Apply light coat of oil to guide bar and wrap it in paper. Clean exterior of the saw. Re- move the spark plug and pour one tea- spoon of two-cycle engine oil or a rust inhibitor product into the combustion chamber. Install spark plug and pull starter rope slowly several times to dis- tribute the oil over the cylinder. Store the saw in a dry, well-ventilated place away from corrosive agents such as gar- den chemicals and fertilizer. Tb remove saw from storage, remove spark plug and pull starter rope several times to clear cylinder of excess oil. Clean and gap spark plug or install a new spark plug. Install guide bar and chain and adjust chain to proper tension. Fill fuel tank with fresh fuel/oil mixture. Do not use old fuel that has been stored more than 90 days. Fill chain oil tank with clean chain oil. 11

CARBURETOR SERVICE CHAIN SAW CARBURETOR SERVICE TROUBLESHOOTING ENGINE OPERATIONAL SYMP- TOMS. Refer to Fig. TR1 for schematic view of typical diaphragm carburetor showing location of parts. Normally en- countered difficulties resulting from carburetor malfunction, along with possible causes of difficulty, are as follows: A. ENGINE WILL NOT START OR HARD TO START. Could be caused by: (1) incorrect idle mixture screw adjustment, (2) restricted or plugged fuel filter or fuel line, (3) throttle shaft worn, (4) choke shaft worn or not functioning properly, (5) inlet needle valve stuck closed, (6) metering lever worn, bent, binding, or set too low, (7) metering diaphragm cover vent hole restricted or plugged, (8) metering diaphragm, gasket or cover leaking, (9) low speed fuel passages restricted or plugged. B. CARBUR] caused by: (1) preventing inl< ing, (2) damag< die and/or seal ing of needle, (J not seated coi (4) metering H high, (5) hole Welch plug in Also, when fu< carburetor, floi leaking fuel pi !TOR FLOODS. Could be irt or foreign particles fuel needle from seat- or worn fuel inlet nee- ireventing proper seat- diaphragm lever spring Jctly on diaphragm lever, jver binding or set too pump diaphragm, (6) Ifuel chamber is loose, tank is located above ding can be caused by p diaphragm. C. ENGINE caused by: (1) (2) restricted fit high speed f hole in fuel metering lever or set too low, screw incorrect pulse passage, (8 carburetor anc :UNS LEAN. Could be iel tank vent plugged, il filter or fuel line, (3) •assages restricted, (4) stering diaphragm, (5) n, binding, distorted high speed mixture [y adjusted, (7) leak in leaky gaskets between cylinder intake port. Also, check for leaking crankshaft seals, porous or cracked crankcase or other cause for air leak into crankcase. D. ENGINE WILL NOT ACCELER- ATE SMOOTHLY. Could be caused by: (1) idle or main fuel mixture screws set too lean on models without accelerating pump, (2) inoperative accelerating pump, on carburetor so equipped, due to plugged channel, leaking diaphragm, stuck piston, etc., (3) restricted low speed fuel passage, (4) restricted tank vent, fuel filter or fuel line, (5) plugged air filter, (6) restricted vent hole in metering cover, (7) restricted pulse channel, (8) defective pump diaphragm, (9) metering lever set too low, (10) defective manifold or carburetor mounting gaskets. E. ENGINE STOPS WHEN DE- CELERATING. Could be caused by: (1) ;o Throttle shutter cocke fast idle ! causing Welch plug loose causing flooding Welch plug loose causing engine to run rich with main adj. closed Flange gasket defective, engine, speeds up and idle is very lean and erratic Impulse channel plugged causing. inoperative fuel pump Dirt in idle system causing. erratic idle Dirt in removable metering jet causing lean operation & no power Dirt in main system causinc lean operation Inlet connection gasket not sealing causing lean operation Hole in metering diapti causing lean operation| Fig. TR1—Schematic cross-sectional view of a dlaphr Filter plug screw gasket leaking causing lean operation Plugged filter causing lean operation Dirt under inlet needle causing flooding Low lever setting causes lean operation and poor acceleration Lever binding on fulcrum pin causes flooding or lean operation High lever setting causes flooding or lean operation Body gaskets defective causing lean operation Body screws loose causing lean operation igm Hole in pump diaphragm causing rich operation type carburetor Illustrating possible causes of malfunction. 12

SERVICE MANUAL CARBURETOR SERVICE idle speed, idle mixture or high speed mixture screws incorrectly adjusted, (2) defective pump diaphragm, (3) pulse passage leaking or restricted, (4) air leaks between carburetor and crankcase, (5) throttle shaft worn, (6) metering lever set too high, (7) fuel inlet needle binding. F. ENGINE WILL NOT IDLE. Could be caused by: (1) incorrect adjustment of idle fuel and/or idle speed screws, (2) idle discharge or air mixture ports plugged, (3) fuel channel plugged, (4) fuel tank vent, filter or fuel line restricted, (5) leaky gaskets between carburetor and cylinder intake ports. G. ENGINE IDLES WITH LOW SPEED NEEDLE CLOSED. Could be caused by: (1) metering lever set too high or stuck, (2) fuel inlet needle not seating due to wear or damage, (3) Welch plug covering idle ports not sealing properly. H. ENGINE RUNS RICH. Could be caused by: (1) plugged air filter, (2) low speed or high speed mixture screws incorrectly adjusted or damaged, (3) metering lever worn, binding, distorted or set too high, (4) fuel pump diaphragm defective, (5) fuel inlet needle valve leaking, (6) Welch plug leaking, (7) faulty governor valve (if so equipped). I. ENGINE HAS LOW POWER UN- DER LOAD. Could be caused by: (1) main mixture screw incorrectly adjusted, (2) plugged fuel tank vent, filter or fuel line, (3) pulse channel leaking or restricted, (4) defective pump diaphragm, (5) plugged air filter, (6) air leaks between carburetor and crankcase, (7) metering lever distorted or set too low, (8) hole in metering diaphragm or gasket leaking, (9) faulty nozzle check valve. PRESSURE TESTING A hand pump and pressure gauge may be used to test fuel system for leakage when diagnosing problems with diaphragm carburetors. With engine stopped and cooled, first adjust carburetor low-speed and high-speed mixture screws to chain saw manufacturer's recommended initial settings. Remove fuel tank cap and withdraw fuel line out fuel tank opening. Remove strainer on end of fuel line and connect a suitable pressure tester as shown in Fig. CS1. Pres- surize system until 7 psi (48 kPa) is read on pressure gauge. Pressure reading must remain constant. If not, remove components as needed and connect pressure tester directly to carburetor inlet fitting as shown in Fig. CS2. Pressur- ize carburetor until 7 psi (48 kPa) is read on pressure gauge. If pressure reading now remains constant, the fuel line is defective. If pressure reading decreases, then carburetor must be removed for further testing. Connect pressure tester directly to carburetor inlet fitting and submerge carburetor assembly into a suitable container filled with a nonflammable solu- tion or water as shown in Fig. CS3. Pres- surize carburetor until 7 psi (48 kPa) is Fig. CS2—Vlew showing connection of pressure tester directly to carburetor Inlet fitting. Refer to text. read on pressure gage. Observe carburetor and note location of leaking air bubbles. If air bubbles escape from around jet needles or venturi, then inlet needle or metering mechanism is defective. If air bubbles escape at impulse opening, then pump diaphragm is defective. If air bubbles escape from around fuel pump cover, then cover gasket or pump diaphragm is defective. To check inlet needle and metering mechanism, first rotate low and high speed mixture screws inward until lightly seated. Pressurize system until 7 psi (48 kPa) is read on pressure gage. If pressure reading does not remain constant, inlet needle is leaking. If pressure remains constant, depress metering diaphragm with a suitable length and thickness of wire through the vent hole in metering diaphragm cover. This will lift inlet needle off its seat and pressurize the metering chamber. A slight drop in pressure reading should be noted as metering chamber becomes pressurized. If no drop in pressure reading is noted, the inlet needle is sticking. If pressure does not hold after a slight drop, a defective metering mechanism or leaking high or low speed Welch plugs are indicated. To determine which compo- nent is leaking, submerge carburetor as previously outlined. Pressurize carburetor until 7 psi (48 kPa) is read on pressure gage, then depress metering diaphragm as previously outlined. If bubbles escape from hole in metering diaphragm cover, metering diaphragm is defective. If bubbles escape from with- in venturi, determine which discharge port the air bubbles are escaping from to determine which Welch plug is leaking. If low or high speed running problems are noted, the passage beneath the respective Welch plug may be restricted. To test idle circuit, adjust low speed mixture screw to recommended initial setting and rotate high speed mixture screw inward until lightly seated. Pres- surize carburetor until 7 psi (48 kPa) is read on pressure gage. Depress meter- Flg. CS3—Submerge carburetor In a suitable container filled with solvent or water and pressure test as outlined In text. Fig. CS1—Vlew showing connection of pressure tester to fuel tank fuel line. Refer to text. 13

CARBURETOR SERVICE |^\^ r^^*^ ^^X"" ^^ 4 -$^ ^x?^. 6—^*b,"^^ f t v^Y/ s 6 ^ >fr v u s. Jslx1^ ^^-^&g) 1 £ ^r*^^i*~^^~2^ u^jfrlr1 ^^^*\* s 15^>^ 16 ^^=\5 x^"^ S^J_^ , ^^f^ I >^ ^3 / / ^M / \n *n -j^ g 4^^&/ ^^^w 18 '^19 K'! r» F/g. CSS— Exploded view of Bing 48 series carburetor. 1. Pump cover 2. Gasket 3. Pump diaphragm 4. Screen 5. Retainer 6. Return spring 7. Throttle plate 8. Throttle shaft 9. Idle speed screw 10. High speed adjusting screw 11. Low speed adjusting screw fx^-^N^.1 < ^§=^^ < ^ 2 <C^'®^TV'^ XT^'TN^ 7^-—^SS'^^5 ^-X'^'^'^x' 6 8 ^-"Hfl c*^^ ^ 9-^^J^» / 10 ^~^§S^\f ^ v^S^St-^v ^^ 17 \i Vv^j^^^t «Tv3 ^^Jr^ ^^ •^^^'' 3 \4 18 ^^T' 3 ^^ 15 19 x^^C^ ^^^o^ <£*r§^?Sv 21 ""jir^ll^^ * 12. Main jet 13. Gasket 14. Circuit plate 15. Needle valve 16. Pin 17. Screw 18. Screw 19. Metering lever 20. Gasket 21. Metering diaphragm 22. Cover ^<*!&^ / 2 Vo4 13 /« / *% / ^w ^^C ^^v^^ /\X_^Sr 16 ^ F/g. CS6—Exploded view of Bing 49 series carburetor. 1 . Cover 2. Metering diaphragm 3. Gasket 4. Metering lever 5. Spring 6. Main jet 7. Screw 8. Pin 9. Needle valve 10. Fixed jet 11. Throttle plate 12. Low speed mixture screw 14 13. Throttle shaft 14. Idle speed screw 15. High speed mixture screw 16. Choke shaft 17. Choke plate 18. Screen 19. Pump diaphragm 20. Gasket 21. Pump cover ing diaphragm a pressure readir drops off very s dicated. To test just high speed mended initial speed mixture s seated. Pressur press metering ly outlined anc pressure readir drops off very s dicated. Refer to spec section and re defective comp AD, Initial setting ing needles is li MAINTENANC ual. Make final with engine wa: certain that en before perform! a restricted air carburetor setti Adjust idle s gine is idling a gagement speet engine idle any i idle fuel needle formance, keepi as possible (tur mixture). If ne speed screw. To < operate engine and find the r points, and set them. Main fuel justed while ei load to obtain without excessr ate saw with hij lean as engine d lack of lubricatii If idle mixtur be properly adji sibility of plugj expansion plug valve loose or rr valve not seatir inlet control lev< phragm or malf If idle mixtui mixture screw a body for damag buretor flooding If high speed cannot be prop* dirt or plugging improperly ad: malfunctioning main fuel checl damaged or mi speed mixture i tioning fuel pun i previously outlined. If I does not drop off or awly, a restriction is in- high speed circuit, ad- lixture screw to recom- setting and turn low rew inward until lightly ze carburetor and de- liaphragm as previous- note pressure gage. If I does not drop off or 3wly, a restriction is in- fic carburetor service rair defect or renew ment as needed. USTMENT for the mixture adjust- ted in the specific saw Z section of this man- :arburetor adjustment m and running. Make ine air filter is clean g final adjustment, as intake will affect the gs. eed screw so that en- just below clutch en- ; do not try to make lower than this. Adjust ar best engine idle per- ig the mixture as rich i needle out to enrich :essary, readjust idle djust main fuel needle, at wide-open throttle ch and lean drop-off the mixture between needle may also be ad- gine is under cutting >ptimum performance e smoke. Do not oper- i speed mixture set too mage may occur due to n and overheating. is too lean and cannot sted, consider the pos- ed idle fuel passages, for main fuel check ssing, main fuel check I, improperly adjusted r, leaking metering dia- nctioning fuel pump. ; is too rich, check idle id its seat in carburetor . Check causes for car- nixture is too lean and rly adjusted, check for in main fuel passages, isted metering lever, netering diaphragm or valve. Also check for ising packing for high crew and for malfunc- P- CHAIN SAW If high speed mixture is too rich, check high speed mixture screw and its seat for damage. Check for improperly adjusted metering lever or faulty fuel inlet needle valve. Check for faulty gover- nor valve if carburetor is so equipped. Setting or adjusting the metering control lever (metering diaphragm lever height) necessitates disassembly of the carburetor. Refer to the following carburetor sections for adjusting the lever height. BING Models 48 And 49 These carburetors are diaphragm type carburetors with integral fuel pumps. OPERATION. Operation of Bing carburetors is typical of other diaphragm type carburetors. Pressure and vacuum impulses from engine crankcase actuate the fuel pump diaphragm. Movement of the diaphragm draws fuel out of the tank to the carburetor fuel pump chamber. A metering diaphragm regulates the amount of fuel that is delivered to the engine. Engine suction is transmitted through the fuel ports in the carburetor air passage to the fuel side of the metering chamber. Atmospheric pressure on the dry side of metering diaphragm then pushes the diaphragm to- ward the fuel metering lever, which opens the fuel inlet needle valve. Fuel from the fuel pump flows past the needle valve into the metering chamber. The fuel in the metering chamber is then drawn through the idle or high speed adjusting orifices and out the idle discharge holes or main nozzle in carburetor air passage by engine suction. OVERHAUL. Clean carburetor exter- nally prior to disassembly. Refer to Fig. CSS and CS6 and disassemble carburetor. Clean and inspect all components. Sharp objects should not be used to clean orifices or passages as fuel flow may be altered. Check metering diaphragm and fuel pump diaphragm for punctures or tears that may affect operation. Examine fuel inlet valve and seat for wear or damage. Fuel mixture screws must be renewed if grooved or broken. Inspect mixture needle seats in carburetor body and renew body if seats are damaged or excessively worn. When reassembling carburetor, renew all gaskets. Diaphragm lever (19—Fig. CSS) should be flush with circuit plate (14) on 48 series carburetors.

SERVICE MANUAL CARBURETOR SERVICE DELL'ORTO Model FTR-16-12 Dell'Orto carburetor Model FTR-16-12 is a diaphragm type carburetor with an integral fuel pump. OPERATION. Operation of Dell'Orto carburetor Model FTR-16-12 is typical of other diaphragm type carburetors. In- let needle valve (14-Fig. CS7), low and high speed mixture screws (5 and 6) and metering diaphragm (2) are incorpor- ated into metering block (4) which can be separated from carburetor body (10). OVERHAUL. Clean carburetor ex- ternally prior to disassembly. Refer to Fig. CS7 and disassemble carburetor. Clean and inspect all components. In- spect metering diaphragm (2) and fuel pump diaphragm (23) for punctures or tears which may affect operation. Ex- amine fuel inlet valve (14) and seat. Inlet valve is renewable, but metering block (4) must be renewed if needle seat is excessively worn or damaged. Sharp objects should not be used to clean orifices or passages as fuel flow may be altered. Fuel mixture screws (5 and 6) must be renewed if grooved or broken. Inspect mixture needle seats in metering block (4) and renew metering block if seats are damaged or excessively worn. To reassemble carburetor, reverse order of disassembly. Renew gaskets (3, 7 and 25). Diaphragm lever (11) should be flush with chamber floor. TILLOTSON Models HC, HJ And HL Tillotson Model HC, HJ and HL carburetors are diaphragm type carburetors with Model HL having an integral diaphragm fuel pump. Operation and servicing of these carburetors is similar and covered in the following paragraphs. OPERATION. Operation of Model HL carburetor is outlined in the following paragraphs. Operation of HC and HJ carburetors is similar to HL but they are not equipped with a diaphragm fuel pump. A cross-sectional schematic view of a typical Tillotson Series HL diaphragm type carburetor with integral fuel pump is shown in Fig. CS9. The top of the pump diaphragm is vented to the engine crankcase through the channel (8). As the diaphragm pulsates, fuel is drawn in- to the carburetor through inlet (1), there is not enough air passing through venturi (14) to create any vacuum on main jet (15). A vacuum is created at primary idle jet (10A), however, and the fuel necessary for running the engine is drawn through that jet. As the throttle disc is opened, enough vacuum is created on secondary idle jet port (10B) so fuel is drawn through that port also. At a certain point, the throttle disc is open far enough so the velocity of air passing through the venturi is suffi- cient to lower the pressure at main fuel discharge port (15) so fuel will flow through this port also. Opening the throttle disc farther results in, higher air velocities and lower venturi pressures 27 screen (28) and pump inlet valve (3A). The fuel is then pumped through outlet valve (3B) into supply channel (17). Engine suction through main jet (15) and idle jets (10) is transmitted to the top of the carburetor diaphragm (25) and atmospheric pressure through vent (23) pushes upward on the diaphragm (25) overcoming spring (20) pressure and unseating inlet needle (18) allowing fuel to flow into diaphragm chamber (6). When starting an engine, closing choke disc (16) increases the vacuum in the carburetor throat so the carburetor will function at the low cranking rpm. When the engine is idling, the throttle disc is almost completely closed and Fig. CS7—Exploded view of Dell'Orto Model FTR-16-12 carburetor. 1. Cover 2. Metering diaphragm 3. Gasket 4. Metering block 5. Low speed mixture screw 6. High speed mixture screw 7. Gasket 8. Screen 9. High speed valve 10. Body 11. Diaphragm lever 12. Pin 13. Spring 14. Fuel inlet valve 15. Throttle plate 16. Throttle shaft 17. Bushing 18. Return spring 19. Bushing 20. Retainer 21. Fuel inlet fitting 22. Screen 23. Fuel pump diaphragm & check valves 24. Idle speed screw 25. Gasket 26. Fuel pump cover 27. Plate 1. Fuel inlet 2. Pump body 3. Pump diaphragm 3A & B. Pump valves 4. Gasket 5. Gasket 6. Metering chamber 7. Idle needle 8. Impulse channel 9. Idle fuel orifice 10. Idle ports 11. Throttle shutter 12. Main fuel orifice 13. Body 14. Venturi 15. Main fuel port 16. Choke shutter 17. Inlet channel 18. Inlet valve 19. Main needle 20. Spring 21. Diaphragm lever 22. Fulcrum pin 23. Vent hole 24. Cover 25. Diaphragm 26. Atmospheric chamber 27. Gasket 28. Screen 29. Screw 30. Fuel chamber 31. Pulse chamber 32. Strainer cover Fig. CS9—Cross-sectional schematic view of Tillotson Series HL diaphragm carburetor. Some models of this type carburetor are equipped with an accelerator pump. _^r\ ^*c ^ \ V 14 15

CARBURETOR SERVICE 1 2 3 F/'g. CS10-Exploded view of Tillotson Model HC carburetor. Model HJ is similar. 1. Throttle plate 2. Lever pin 3. Body 4. Return spring 5. Throttle shaft 6. Choke shaft 7. Choke plate 8. Idle mixture screw 9. High speed mixture screw 10. Choke friction pin 11. Fuel inlet valve assy. 12. Spring 13. Diaphragm lever 14. Idle speed screw 15. Gasket 16. Metering diaphragm 17. Cover Fig. CS11 - Exploded view of Tillotson Model HL carburetor. On some HL carburetors, pump diaphragm (19) and valves (20) are one-piece. Gover- nor valve (25) is not used on all carburetors. 1. Throttle plate 13. Idle speed screw 2. Lever pin 14. Choke plate 3. Body 15. Gasket 4. Throttle return 16. Metering diaphragm spring 17. Diaphragm cover 5. Idle mixture screw 18. Gasket 6. Drain plug 19. Fuel pump diaphragm 7. High speed mixture 20. Fuel pump valves screw 21. Pump body 8. Choke detent 22. Screen 9. Gasket 23. Gasket 10. Fuel inlet valve assy. 24. Fuel inlet 11. Spring 25. Governor valve 12. Diaphragm lever 26. Diaphragm lever pin that increase;! the flow of fuel out of the discharge Any vacuuih created at idle discharge ports (10) on main fuel discharge port (15) is transferred through metering chamber (6) to diaphragm (25). Air pressure entering through atmospheric vent hole (fe) pushes against the diaphragm because of the vacuum and overcomes pnessure applied by spring (20) through control lever (21). This releases inlel needle valve (18) and allows fuel to enter the metering chamber in a direct relationship to the vacuum creaned at the fuel discharge ports. The Higher the vacuum, the greater the movement of the diaphragm and the largen the opening of the needle valve. Thus, reel is metered into the carburetor to meet the needs of the engine. Some HL carburetors are equipped with governd| valve (25-Fig. CS11) which enricheis the fuel mixture at the governed speld and prevents engine overspeeding. Original governor assembly is tuned for each engine and cannot be renewed. M disc may be installed in place of governor assembly. OVERHAU) carburetor is buretor, overt Model HL will Models HC an] carburetor wit| pump. Refer td Since the Model HL ie most widely used car- [aul procedures for the be covered. Overhaul of HJ is similar to the HL the exception of the fuel Figs. CS10 and CS11. DISASSEMBLY. Clean carburetor and inspect for signs of external damage. Remove idle speed screw and inspect screw, [washer and spring. In- spect threads in carburetor body for damage and repair with a Heli-Coil insert, if necessaf Remove the ffter cover, cover gasket, and filter screen. Clean filter screen by flushing with sdlvent and dry with compressed air. The cover gasket should be renewed whenever filter screen is serv- iced. Clean all ||dirt from plastic cover before assembly Remove the llsix body screws, fuel pump cover casting, fuel pump diaphragm and gaiket. Diaphragm should be flat and free from holes. The gasket \. ill 1111 Fig. CS12—Diaphragm lever should be flush with diaphragm chamber floor. CHAIN SAW should be renewed if there are holes or creases in the sealing surface. Remove the diaphragm cover casting, metering diaphragm and diaphragm gasket. Inspect the diaphragm for holes, tears and other imperfections. Remove the fulcrum pin, inlet control lever and inlet tension spring. Care must be used while removing parts due to spring pressure on inlet control lever. The spring must be handled carefully to prevent stretching or compressing. Any alteration to the spring will cause improper carburetor operation. If in doubt as to its condition, renew it. Remove inlet needle. Remove inlet seat assembly using a 5/16 inch thin wall socket. Remove the inlet seat gasket. Inlet needles and seats are in matched sets and should not be interchanged. Needle and seat assembly must be clean for proper performance. Use a new gasket when installing the insert cage. Do not force cage as threads may be stripped or the cage distorted. Use a tor- que wrench and tighten cage to 25-30 in.-lbs. (2.8-3.4 N-m). Remove both high speed and idle mixture screws and inspect points. Notice the idle mixture screw point has the step design to minimize point and casting damage. The mixture screws may be damaged from being forced into the casting seat or possibly broken off in the casting. They may be bent. If damage is present be sure to inspect condition of casting. If adjustment seats are damaged, a new body casting is required. ASSEMBLY. Install the main nozzle ball check valve if this part was found to be defective. Do not overtighten as dis- tortion will result. Install new Welch plugs if they were removed. Place the new Welch plugs into the casting counterbore with convex side up and flatten it to a tight fit using a 5/16 inch flat end punch. If the installed Welch plug is concave, it may be loose and cause an uncontrolled fuel leak. The correctly installed Welch plug is flat. Install inlet seat and tighten to 25-30 in.-lbs. (2.8-3.4 N-m). Install inlet needle. Install inlet tension spring, inlet control lever, fulcrum pin and fulcrum pin retain- ing screw. The inlet control lever must rotate freely on the fulcrum pin. Adjust inlet control lever so the center of the lever that contacts the metering diaphragm is flush to the metering chamber floor as shown in Fig. CS12. Place metering diaphragm gasket on the body casting. Install metering diaphragm next to gasket. Reinstall diaphragm cover casting over metering diaphragm and gasket. Install pump gasket on diaphragm cover first, then the fuel pump diaphragm should be assembled next to the gasket and the flap valve 16

SERVICE MANUAL CARBURETOR SERVICE member next to the fuel pump diaphragm so that the flap valves will seat against the fuel pump cover. Reinstall fuel pump cover and attach with six body screws. The above parts must be assembled in the proper order or the carburetor will not function properly. Install filter screen on fuel pump cover. Install gasket on filter screen and replace filter cover over filter screen and gasket and attach with center screw. Install high speed and idle mixture screws in their respective holes being careful not to damage points. Welch plugs seal the idle bypass ports and main nozzle ball check valve from the metering chamber. Removal of these plugs is seldom necessary because of lack of wear in these sections and any dirt that may accumulate can usually be blown out with compressed air through the mixture screw holes. If removal of the Welch plugs is necessary, drill through the Welch plug using a V8-inch drill bit. Allow the drill bit to just break through the Welch plug. If the drill bit travels too deep into the cavity, the casting may be ruined. Pry the Welch plug out of its seat using a small punch. Inspect the idle bypass holes to ensure they are not plugged. Do not push drill bits or wires into the metering holes. This may damage the flow characteris- tics of the holes and upset carburetor performance. Blow out plugged holes with compressed air. Remove main nozzle ball check assembly with a screw- driver of correct blade width. If ball check is defective, engine idling will be hampered unless high speed mixture screw is shut off or there will be poor high speed performance with high speed mixture screw adjusted at 1V4 turns open. Replace the ball check if defective. Removing choke and throttle plates before cleaning the body is not necessary if there is no evidence of wear. In- dication of wear will require the removal of plates to check the casting. To remove the plates, first mark the position of the plates on their respective shafts to assure correct reassembly. The plates are tapered for exact fit in the carburetor bore. Remove two screws and pull the plate out of the carburetor body. Remove the throttle shaft clip and pull the shaft out of the casting. Examine both the shaft and body bearing areas for wear. Should either part show wear then either the shaft or the body or both will have to be renewed. Remove the choke shaft from the body carefully so the friction ball and spring will not fly out of the casting. Inspect the shaft and bushings for wear. Model HK Tillotson Model HK carburetor is a diaphragm type with an integral diaphragm type fuel pump. OPERATION. Operation of Tillotson Model HK is basically similar to that described for the Tillotson HL carburetor in preceding section, the main difference being that the Series HK carburetor is a compactly designed unit usually used on lightweight, small displacement engines. OVERHAUL. Carburetor may be dis- assembled after inspecting unit and referral to exploded view in Fig. CS13. Clean components using a suitable solvent and compressed air. Do not attempt to clean metered passages with drill bits or wire as carburetor performance may be affected. Inspect inlet lever spring (20) and renew if stretched or damaged. Inspect diaphragms for tears, cracks or other damage. Renew idle and high speed adjusting needles if needle points are grooved or broken. Carburetor body must be renewed if needle seats are damaged. Fuel inlet needle has a rubber tip and seats directly on a machined orifice in circuit block (19). Inlet needle or circuit block should be renewed if excessively worn. With circuit block components installed, note height of long end of diaphragm lever (21). Lever end should be flush with chamber floor in circuit block. Bend lever adjacent to spring to obtain correct lever height. Models HS, HT And HU Tillotson Models HS, HT and HU carburetors are diaphragm type with integral diaphragm type fuel pumps. Op- eration and servicing of HS, HT and HU carburetors are similar and covered in the following paragraphs. OPERATION. A cross-sectional schematic view of a Tillotson Series HS carburetor is shown in Fig. CS14. Op- eration of Models HS, HT and HU carburetors is basically similar to that described for the Tillotson HL carburetor in OPERATION section of Models HC, HJ and HL section. Some Model HS carburetors are equipped with a governor valve (26—Fig. CS15), consisting of a check ball and spring. The governor valve resonates at a desired engine speed that allows excess fuel to bypass the check ball and enter directly into carburetor bore. The rich fuel mixture causes the engine to lose power and slow down, thereby preventing overspeeding. OVERHAUL. Refer to appropriate exploded view of carburetor shown in Fig. CS15, CS15A or CS16. Thoroughly clean outside of carburetor prior to disassem- Fig. CS13-Exploded view of Tillotson Model HK carburetor. 1. Pump cover 2. Gasket 3. Fuel pump diaphragm & valves 4. Screen 5. Throttle plate 6. Throttle shaft 7. Throttle return spring 8. Idle speed screw 9. Spring 10. Spring 11. Idle mixture screw 12. High speed mixture screw 13. Spring 14. Detent hall 15. Choke plate 16. Screen 17. Retainer 18. Gasket 19. Circuit block 20. Spring 21. Diaphragm lever 22. Fuel inlet needle 23. Lever pin 24. Gasket 25. Metering diaphragm 26. Cover 27. Choke shaft 28. "E" ring 17

CARBURETOR SERVICE CHAIN SAW bly. Remove pump cover and metering Inspect mete] chamber cover for access to internal new if stretchel components. Clean filter screen (4—Fig. aphragms for t( CS17). Welch plugs may be removed by age. Renew prying out with a sharp punch as shown adjusting need] in Fig. CS19. Use care not to damage car- grooved or bn buretor casting when removing Welch must be rene^ plugs. Clean components using solvent damaged. Fuel and compressed air. Do not attempt to ber tip and seat!) clean passages with drill bits or wire as orifice in carbi carburetor calibration may be affected body should b< if passages are enlarged. let needle is d; ing lever spring and re- or damaged. Check di- cracks or other dam- le and high speed s if needle points are en. Carburetor body d if needle seats are nlet needle has a rub- directly on a machined tor body. Carburetor renewed if seat for in- aged. Carburetor may be reassembled by reversing disassembly procedure. Adjust position of metering lever so lever is flush with diaphragm chamber floor as shown in Fig. CS20. Bend lever adjacent to spring to obtain correct lever position. Note that on some HS carburetors the metering diaphragm is hooked to the metering lever. WALBRO 28 fig. CS14—Cross-sectional \lew of typical Series HS Til- jtson diaphragm-type carburetor. 1. Filter screen 2. Venturi 3. Pulse chamber 4. Fuel chamber 5. Pump diaphragm 5A. Inlet valve 5B. Outlet valve 6. Pump body 7. Gasket 8. Inlet fitting 9. Impulse channel 10. Throttle plate 11. Primary (A) & secondary (B) idle ports 12. Main fuel orifice 13. Idle fuel needle 14. Carburetor body 15. Metering chamber 16. Idle fuel orifice 17. Metering diaphragm 18. Atmospheric chamber 19. Vent hole 20. Diaphragm cover 21. Spring 22. Fulcrum pin 23. Gasket 24. Diaphragm lever 25. Inlet valve 26. Main fuel needle 27. Choke disc 28. Inlet channel 29. Main fuel port \ig. CS15-Exploded view \t Tillotson Model HS carburetor. 1. Pump cover 2. Gasket 3. Fuel pump diaphragm & valves 4. Screen 5. Throttle plate 6. Body 7. Throttle return spring 8. Idle mixture screw 9. High speed mixture screw 10. Idle speed screw 11. Spring 12. Choke friction ball 13. Choke plate 14. Fuel inlet valve 15. Spring 16. Screen 17. Screen retainer 18. Welch plug 19. Diaphragm lever 20. Lever pin 21. Gasket 22. Metering diaphragm 23. Cover 24. Welch plug 25. Gasket 26. Governor 27. Choke shaft 28. Throttle shaft 29. Check valve Models HD, HDA, HDB, HOC And SDC Walbro carburetor Models HD, HDA, HDB, HOC and SDC are diaphragm type carburetors with integral diaphragm type fuel pumps. Some carburetors are also equipped with an accelerator pump. Model number on Model HD, HDA, HDB or HOC carburetor is found on side of carburetor adjacent to fuel mixture adjusting screws. Model number on Model SDC carburetors is stamped on bottom of carburetor. OPERATION. In Fig. CS21, a cross- sectional schematic view of a Walbro 15 Fig. CS15A—Exploded view of Tillotson Model HT carburetor. 1. Fuel pump cover 2. Gasket 3. Pump diaphragm 4. Throttle plate 5. Throttle shaft 6. Choke shaft 7. Idle speed screw 8. Low speed mixture needle 9. High speed mixture needle 10. Valve jet 11. Cup plug 12. Pin 13. Metering diaphragm 14. Gasket 15. Cover 16. Metering lever 17. Fuel inlet needle 18. Main jet 19. Choke plate 20. "E" rings 21. Washer 22. Filter 18

SERVICE MANUAL CARBURETOR SERVICE Series SDC carburetor is shown. Opera- tion of Models HD, HDA, HDB and HDC is similar to Model SDC and discus- sion will also apply to Models HD, HDA, HDB and HDC except for explanation of Model HDC accelerator pump. Except for some models, Model SDC carburetor is equipped with an accelerator pump. When throttle is open, indexing hole in throttle shaft (25-Fig. CS21) opens pulse passage (4) to accelerator pump passage (8). Pressure against pump diaphragm (9) compresses spring (10) and pressurizes fuel passage (11), ejecting excess fuel from main nozzle (27). When throttle is closed, or partially closed, indexing hole closes pulse passage and accelerator pump spring returns diaphragm to original position, drawing fuel back up passage (11) to re- charge accelerator pump. At idle speed, air is drawn into carburetor through air bleed hole (13) and mixed with fuel from idle fuel passage in what is called the "emulsion channel." More air enters idle fuel cavity through Fig. CS16—Exploded view of Tillotson Model HU carburetor. Note difference in idle speed screw location used on fuel pump covers (3 and 3A) of some carburetors. Idle speed screw (25) may be located in cover (24). 1. Idle speed screw 2. Friction ball 3. & 3A. Fuel pump cover 4. Screen 5. Gasket 6. Fuel pump diaphragm & valves 7. Throttle plate 8. Return spring 9. Throttle shaft 10. Body 11. "E" ring 12. Idle mixture screw 13. High speed mixture screw 14. Nozzle check valve 15. Screen 16. Retainer 17. Cup plug 18. Fuel inlet valve 19. Spring 20. Diaphragm lever 21. Lever pin 22. Gasket 23. Metering diaphragm 24. Cover 25. Idle speed screw 26. Idle speed screw 27. Welch plug the two idle holes (24) nearest venturi and the fuehair mixture is ejected from the third idle hole. Air cannot enter the main fuel nozzle (27) as the check valve (15) closes against its seat when engine is idling. Note that idle fuel supply must first pass main (high speed) metering needle (14) before it reaches idle fuel needle (22). Model HDC carburetors with accelerator pump, except HDC 70, have a pulse passage (P-Fig. CS22) in carburetor body which allows crankcase pulsations to enter idle fuel circuit. The pulse passage is opened and closed by throttle Fig. CS17—Be sure to clean filter screen (4 —Fig. CS15 or CS16) when servicing carburetor. Fig. CS19 —A punch can be used to remove Welch plugs as shown. INLET CONTROL LEVER SET FLUSH WITH CHAMBER FLOOR METERING CHAMBER FLOOR 18 Fig. CS20—Diaphragm lever on Tillotson Models HS, HT and HU should be flush with diaphragm chamber floor as shown above. Fig. CS18—View showing location of Welch plugs (18 & 24-Fig. CS15). 1. Fuel inlet 2. Surge chamber 3. Inlet check valve 4. Crankcase pulse channel 5. Fuel pump diaphragm 6. Outlet check valve 7. Fuel filter 8. Accelerator pulse channel 9. Accelerator diaphgram 10. Accelerator spring 11. Accelerator fuel channel 12. Choke disc 13. Idle air bleed channel 14. Main (high speed) fuel needle 15. Main orifice check valve 16. Inlet needle 17. Metering lever 18. Metering diaphragm 19. Atmospheric vent 20. Metering diaphragm spring 21. Idle fuel channel 22. Idle fuel needle 23. Idle fuel passage 24. Idle air and fuel holes 25. Throttle shaft 26. Throttle disc 27. Main fuel orifice Fig. CS21 —Cross-sectional schematic view of Walbro Series SDC carburetor with accelerator pump. Some models are not equipped with accelerator pump and passages (8 and 11) are plugged. Fuel cavity above metering diaphragm extends to cavity shown at tip of main fuel needle (14). 19

HOMELITE CHAINSAW Repair Manual

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