Professional Shop Handbook - JustAnswer

Professional Shop Handbook

32cc Engine with Auto-Choke

MTD Products Inc - Product Training and Education DepartmentFORM NUMBER - 769-02773

10/2006

NOTE: These materials are for use by trained technicians who are experienced in the service and repair of outdoor power equipment of the kind described in this publication, and are not intended for use by untrained or inexperienced individuals. These materials are intended to provide supplemental information to assist the trained technician. Untrained or inexperi-enced individuals should seek the assistance of an experienced and trained professional. Read, understand, and follow all instructions and use common sense when working on power equipment. This includes the contents of the product’s Oper-ators Manual, supplied with the equipment. No liability can be accepted for any inaccuracies or omission in this publication, although care has been taken to make it as complete and accurate as possible at the time of publication. However, due to the variety of outdoor power equipment and continuing product changes that occur over time, updates will be made to these instructions from time to time. Therefore, it may be necessary to obtain the latest materials before servicing or repairing a product. The company reserves the right to make changes at any time to this publication without prior notice and without incurring an obligation to make such changes to previously published versions. Instructions, photographs and illustrations used in this publication are for reference use only and may not depict actual model and component parts.

© Copyright 2006 MTD Products Inc. All Rights Reserved

I

1. INTRODUCTION ........................................................................................................................12. PERIODIC MAINTENANCE........................................................................................................13. INITIAL TROUBLESHOOTING...................................................................................................24. AUTO-CHOKE ..........................................................................................................................13

Table of Contents

32cc engine with Auto-Choke

1

1. INTRODUCTION

1.1. Disclaimer: This service manual was intended for use by trained technicians. The information contained in this manual is current and accurate at the time of writing, but is subject to change without notice.

1.2. The 32cc engine at first glance appears the same as other 2 cycle trimmer power heads. The only visible difference is the manual choke lever was removed and a mechanical automatic choke was introduced. See Figure 1.2.

1.3. Features included with this model are:

• Automatic choke

• 32cc displacement (1.952 Cubic Inches)

• Electronic- Max Fire Ignition ™

• Incredi-pull ™ Starting

• Fuel capacity 13oz (384ml)

• Cantilever crank

Figure 1.2

2. PERIODIC MAINTENANCE

2.1. Periodic Maintenance is a key factor in keeping any piece of Outdoor power products running at optimum and avoiding service work or possible catastrophic damage.

• Air Filter: Check the air filter on a regular basis, A dirty air filter can drastically effect the opera-tion of any engine. from ingesting dirt or debris to blocking the flow of air into the carburetor.

• Spark Plug: Damaged or fouled spark plug can deprive optimum output and can indicate several different conditions Think of a spark plug the same way you think of batteries in a smoke detector. They may seem to be okay but its best to change them annually.

• Fuel: Always burn the fuel out of any piece of equipment that may be sitting for any length of time. Confirm that there is a proper Oil/fuel mix (40:1). Agitate the fuel container prior to filling the fuel tank or agitating the fuel tank prior to starting the engine.

• Clean: In order for the engine to operate at an acceptable temperature. Make sure that the exterior of the engine is clean and allowing good air flow. The fins that are on the engine head need to be clean of all foreign debris.

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2

3. INITIAL TROUBLE SHOOTING

NOTE: Common reasons that cause any engine failure are due to introduction or ingestion of abrasive material, insufficient lubrication, over-heating, over speeding, and breakage (wear).

NOTE: Prior to doing any service work try to obtain as much information from the customer as possible to help determine where to begin your diagnosis.

3.1. Keeping in mind that there are five events that occur in every properly operating engine. Each event must occur precisely at the right time in order for the engine to operate correctly.

• Intake: The fuel mix is drawn into the combus-tion chamber from the crankcase due to pres-sure changes created by the piston movement.

• Compression: The fuel/air mix needs to be compressed to heat the mixture and convert the mix into a more volatile state in order to be ignited correctly for timely and more effective burn.

• Ignition: As the magnets on the flywheel pass by the magneto armatures. A small current, 200 volts, is produced inside of the magneto. As the current travels through the primary and second-ary windings the current is increased to 20,000 volts.

• Power: When the fuel mixture is introduced into the combustion chamber and the spark is cre-ated the mixture combust and rapidly expands forcing the piston towards the crank shaft. this movement is transferred to the crankshaft then on to the application.

• Exhaust: After the fuel mixture has been ignited the burnt gasses remaining are forced towards the crankshaft the exhaust port opens allowing the exhaust gasses to escape out of the com-bustion chamber.

NOTE: There are two types of screws used on the engine and housing. Screws that fasten into Plastic and screws that fasten into the cast. See Figure 3.1.

INTAKE

3.2. If the engine does not start, by systematically fol-lowing a sequence the failure can be found rela-tively quick.

3.3. Start with the most obvious and work your way through the engine.

• Inspect the fuel tank for of debris.

• Determine if the fuel tank/cap is venting.

• Check to see if fuel is getting into the cylinder.

3.4. Detach the air cleaner housing by removing the the four T-20 perimeter screws.

Figure 3.1

Plastic Fastener

Cast fastener


3

3.5. Inspect the air filter for debris. If the air filter is dirty clean with warm water and soap, dry, add a light film of oil, and re-install. See Figure 3.5.

NOTE: If the Air filter shows signs of deteriora-tion replace with a new filter

3.6. If an air filter was not on the machine there may be severe internal engine damage.

3.7. Drain the fuel into a clear glass container and inspect the fuel for:

• Debris

• Discoloration

• Water.

Figure 3.5

3.8. Most 2 cycle oil use a die or coloring agent so it is possible to tell if oil has been mixed with the fuel. Recently there have been synthetic oils introduced that do not have a die included this could mislead a technician. See Figure 3.8.

3.9. If the fuel has a foul odor or smells like varnish assume stale fuel. Drain the fuel in an accept-able container and depose of fuel according to your local laws.Then replace with a fresh fuel and oil mix (40:1).

3.10. If the fuel was bad save a sample for the cus-tomer to educate them about the importance of maintaining fresh fuel in their equipment and suggest a fuel additive that can extend the life of the fuel.

Figure 3.8


4

3.11. If debris was found in the fuel, check the fuel fil-ter to determine if it may need replacing. The fuel filter is located in the fuel tank. See Figure 3.11.

3.12. If the fuel filter is dark brown in color replace fuel filter.

3.13. To access the fuel filter remove the rear air filter housing.

3.14. Remove the Carburetor / choke plate with a T-20 driver. See Figure 3.14.

3.15. Remove the four carburetor mounting screws.

3.16. Pull the fuel lines through the carburetor mount-ing housing. See Figure 3.16.

3.17. Separate the fuel line from the fuel line adaptor. See Figure 3.17.

3.18. Pry the sealing grommet that secures and seals fuel line to the fuel tank.

Figure 3.11

Fuel Filter

Figure 3.14

CarburetorChoke platemounting screws

Carburetor/Choke Plate

Figure 3.16

Carburetor Mounting Screws

Figure 3.17

Fuel line adaptor

Sealing Grommet


5

3.19. Push the filter into the fuel tank and remove the filter and line from the fuel tank. See Figure 3.19.

3.20. Take a moment to inspect the fuel line if cracking or signs of wear are apparent replace the filter and fuel line.

NOTE: The filter and fuel lines all come together as one assembly.

3.21. Detach the fuel line from the fuel filter.

3.22. If the filter is dirty or clogged replace with a new filter. Inspect filter stem for any debris. See Figure 3.22.

Figure 3.19

Figure 3.22

Filter

Filter Stem

3.23. To replace fuel filter and fuel line:

3.24. Use approximately 10” of .080 trimmer line to re-install fuel line.

3.25. Feed the trimmer line up through the fuel tank from the hole that the fuel filter mounts. See Figure 3.25.

3.26. Pull the trimmer line and fuel line through. See Figure 3.26.

Figure 3.25

.080Trimmer Line

Figure 3.26

Inner Hole

Outer Hole


6

3.27. When the fuel line starts coming through the hole in the fuel tank pull the fuel line and the filter with your finger. See Figure 3.27.

3.28. Slide the grommet onto the fuel line while push-ing the grommet pull the filter until the grommet is tight against the fuel tank. See Figure 3.28.

3.29. Re-install the Dark colored return line and re-assemble in reverse order.

3.30. Inspect the Atmospheric vent hole on the dia-phragm cover for debris. See Figure 3.30.

3.31. Inspect the throttle and choke levers for debris or anything that may interrupt proper function.

3.32. Disassemble the carburetor. Inspect the dia-phragm and seals for signs of deterioration and inspect the fuel pump and seals. See Figure 3.32.

Figure 3.27

Figure 3.28

Figure 3.30

VENT HOLEATMOSPHERIC

Figure 3.32

Metering Diaphragm

Fuel Pump and Seal

Diaphragm Cover


7

3.33. Inspect the metering needle valve for wear or debris. See Figure 3.33.

3.34. Inspect the needle metering valve for signs of deterioration. If there is any signs of deteriora-tion it would be safe to assume that the carbure-tor would need to be replace. See Figure 3.34.

3.35. Re-install by reversing the disassembly instruc-tions.

Figure 3.33

Metering Valve

Figure 3.34

Metering needlevalve seat

3.36. This is a Walbro carburetor that would require adjusting tool p/n 791-500-510. See Figure 3.36.

3.37. If the high and low settings need adjusting remove the adjustment screws and examine them for:

• Corrosion

• damaged carburetor

• or damaged metering seals

3.38. If the seal ends of the Metering screws show signs of wear or damage the carburetor may need replaced. Further inspection is needed. See Figure 3.38.

Figure 3.36

“D” end screws

Figure 3.38

Metering seals


8

3.39. While the metering screws are out of the carbu-retor examine the o-rings located in the ports that the metering screws were removed from. See Figure 3.39.

3.40. When in-stalling the adjustment screws gently screw them in completely. The seating ends of the screws are delicate, and can be damaged easily from over tightening.

3.41. Back the screws out 11/2 turns.

3.42. Finish the adjustment by turning in at 1/8 turn increments.

3.43. Adjust the idle screw so it barely touches the throttle plate lever.

3.44. Idle speed -2800- 3600 RPM

3.45. Operating speed 7200 + RPM

COMPRESSION

3.46. If you have a no start situation or lose of power, by systematically following a sequence can help to expedite locating the failure.

3.47. Check and make sure the spark plug is installed properly.

3.48. Remove the air cleaner housing by removing the four T-20 screws.

3.49. Detach the muffler and with a flash light observe the condition of the piston and piston rings for scoring or gouging. See Figure 3.49.

3.50. If the piston or piston ring appears to be scored no further compression testing is needed.

Figure 3.39

O-rings

Throttle Plate Lever

Idle Screw

Figure 3.49

Piston


9

3.51. If the piston or piston rings appears to be in good condition a compression test should to be per-formed. See Figure 3.51.

NOTE: If the engine compression is below 90psi additional diagnostics is needed.

3.52. Remove the rear air cleaner housing.

3.53. Remove the lower front shroud screw to detach the lower shroud. See Figure 3.53.

Figure 3.51

Figure 3.53

Lower shroudscrew

3.54. Remove the two T-20 screws that hold the choke plate and carburetor in place. See Figure 3.54.

3.55. Remove the four T-20 screws that secure the carburetor mounting assembly. See Figure 3.55.

Figure 3.54

T-20 Screws

Figure 3.55

CarburetorMount Screws


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3.56. Remove the two cylinder screws with a T-30 driver. See Figure 3.56.

3.57. Carefully pull the cylinder from the crankcase. See Figure 3.57.

3.58. Inspect the cylinder for scores or gouges.

3.59. If the cylinder has scores along the cylinder wall the cylinder should be replaced.

NOTE: At this point contact the customer and discuss the cost of repairing to the cost of replacement.

3.60. Inspect the piston for scores or gouges.

3.61. Inspect the needle bearings at the base of the connecting rod for signs of wear or debris. See Figure 3.61.

3.62. Inspect the piston rings for carbon build-up.

3.63. If the Piston ring grove needs cleaning DO NOT use a wire brush.

3.64. The tool of choice to clean the piston ring groves is an old piston ring. The old piston ring is best because you can aggressively clean the carbon from the grove without compromising the sur-face of the piston. See Figure 3.64.

Figure 3.56

Cylinder screws

Figure 3.57

Figure 3.61

Needle Bearings

Figure 3.64

Piece of piston ring


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IGNITION

3.65. If you have a no start situation by systematically following a sequence can help to expedite locat-ing the failure.

3.66. Perform a spark test to determine if the flywheel and magneto are producing a spark to the spark plug. See Figure 3.66.

3.67. Check to see what the spark plug looks like.

• Dry fouled plug could mean the engine is run-ning rich or to much fuel in the mix.

• Wet fouled plug could mean that the engine is running lean or to much oil in the mix.

• White coating could mean that the engine was run without oil or a diluted mix.

3.68. These conditions could be a result of a poor fuel /oil mix or a mis-adjusted carburetor.

3.69. Replace the spark plug with an acceptable replacement.

3.70. Inspect and test the shut off switch to determine that the ground switch is operating.

3.71. Separate the grip by removing the five perimeter screws leave the anti rotation screw in place.

3.72. Disconnect the wires from the shut off switch.

Figure 3.66

3.73. Connect an Ohm meter to the blades of the shut off switch. See Figure 3.73.

NOTE: The blades on the switch are very close take care not to touch the leads.

NOTE: This test can be done without removing the switch by connecting the leads to the red and black wire that run to the magneto.

3.74. With the switch at rest the meter should show no continuity See Figure 3.74.

3.75. The shut off switch is a spring loaded rocker switch.

Figure 3.73

Figure 3.74


12

3.76. Press and hold the switch in the stop position. The meter should show continuity. See Figure 3.76.

3.77. Upon completion of testing the switch make sure that the wires are connected and secure to the blades on the switch and on the magneto.

3.78. Inspect flywheels magnets for magnetism and the flywheel itself for cracks or missing fan blades.

3.79. If there are any cracks replace the flywheel.

3.80. Check the air gap between the magneto arma-ture and the flywheel. See Figure 3.80.

NOTE: If a brass feeler gauge is not available a business card would be a suitable option.

POWER

3.81. Examine the engine notice where debris is and isn’t. If there is a crankcase leak generally there will be an obvious build up of dirt and debris stuck to the oil that has leaked out.

3.82. A compression test can be done.

3.83. A crankcase pressure and crankcase vacuum test can determine if there are any leaks in the seals and gaskets where the different compo-nents of the engine are joined.

Figure 3.76

Figure 3.80

.010 air gap


13

EXHAUST

3.84. Check the spark arrestor on the muffler

3.85. Carbon can build up on the screen to the point of not allowing the burnt gasses to escape out of the muffler, causing loss of power.

3.86. Remove the exhaust port from the bottom of the muffler and check the Spark arrester screen for any carbon build up. See Figure 3.86.

3.87. The screen will become carbonized under nor-mal use and even if the fuel and oil have been properly mixed.

3.88. The mufflers used on 2 cycle products are not only for sound reduction but creates a positive pressure and acts as a expansion chamber to aid in scavenging exhaust from the combustion chamber.

Figure 3.86

Spark Arrestor Screen

Exhaust Port

Muffler

4. AUTO CHOKE

4.1. The auto choke is a mechanical choke that is automatically engaged when the starter rope is pulled. See Figure 4.1.

4.2. When the trigger is squeezed the throttle is then applied to open the choke. See Figure 4.2.

Figure 4.1

Figure 4.2

Trigger


14

4.3. Remove the spark plug and/or ground the igni-tion wire to the engine block. If it is necessary to remove the clutch housing or the clutch rotor insert approximately 12” of starter rope into the combustion chamber. This will act as a piston stop and prevent the crankshaft from turning. See Figure 4.3.

4.4. Remove the five screws that hold the throttle housing together. See Figure 4.4.

4.5. It is unnecessary to remove the anti-rotation screw unless a throttle housing replacement is needed.

4.6. There is a anti-rotation screw found on the bot-tom side of the upper drive shaft assembly. This was mentioned mainly to prevent a technician from damaging the throttle housing during disas-sembly. See Figure 4.6.

4.7. Remove the anti-rotation screw from the side of the clutch cover assembly. See Figure 4.7.

NOTE: Loosen the clamping screw and slide the shaft from the clutch cover assembly. There is no reason to remove the clamping screw.

Figure 4.3

Figure 4.4

Perimeter Screws

Anti-Rotation Screw

Figure 4.6

T-20 Driver

Anti-rotation Screw

Figure 4.7

Anti-rotationScrew

Clamp Screw


15

4.8. Remove the three plastic screws that fasten the clutch housing. See Figure 4.8.

4.9. Remove the clutch drum assembly with a T-20 driver. See Figure 4.9.

Figure 4.8

Clutch housingscrews

Figure 4.9

T20 Driver

4.10. The screw is a standard thread right to tighten and left to loosen. See Figure 4.10.

NOTE: Keep track of the small (.010) thrust washer that is between the clutch and clutch housing.

4.11. Remove the clutch rotor with clutch tool 791-180918 or strap wrench. See Figure 4.11.

NOTE: Rotate the clutch assembly left to remove.

NOTE: Do not use pliers or any tool that can score the contact surface of the clutch.

Figure 4.10

Thrust washer

Clutch housing

Figure 4.11

p/n 791-180918 Tool Clutch


16

4.12. Keep track of the clutch washer. Without this the heat will build up and melt the starter housing.

4.13. Remove the four screws that fasten the starter housing to the casting. There is a fifth screw on the bottom that fastens into the shroud exten-sion. See Figure 4.13.

NOTE: The top four screws mount into the cast-ing and the bottom one mounts into plastic.

4.14. Release the tension on the starter rope prior to disassembling the starter housing.

4.15. Remove the starter housing and lay front down. Remove the three screws that secures the pres-sure plate assembly. See Figure 4.15.

4.16. Remove the Pressure plate assembly to expose the recoil pulley assembly and ACL (Automatic Choke lever) assembly.

4.17. Remove the T-20 screw that secures the Auto-matic choke lever to the starter housing. See Figure 4.17.

4.18. Together Slide the return spring and the Auto-matic choke lever upward . See Figure 4.18.

Figure 4.13

Starter HousingScrews

Figure 4.15

Pressure PlateScrews

Figure 4.17

Figure 4.18


17

4.19. Remove the Palnut (pt# 753-04288) with a screw driver. See Figure 4.19.

4.20. Remove the recoil pulley carefully using caution not to discharge the recoil spring. See Figure 4.20.

Figure 4.19

Palnut

Figure 4.20

4.21. Carefully separate the recoil pulley. See Figure 4.21.

NOTE: Although the pulley can be separated it is sold as one complete assembly.

4.22. When installing the recoil pulley rewind the rope on the recoil pulley leaving enough rope to route through the ACL assembly.

Figure 4.21

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