Yamaha 25BMH Manual Download Page 18 | Manualshive

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TECHNICAL TIPS

1-17

E

GEN

INFO

(3) High engine speed

In the high engine speed where the throttle valve is fully open, the fuel delivered through the
main jet is mixed with the air delivered through the main air jet, which is fed into the venturi
through the main nozzle.
Air/fuel mixture delivery through the bypass holes and the pilot outlet continues in the high
engine speed.

Fig. 13

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Summary of Contents for 25BMH

Page 1: ...F PROTECTION 1 2 OILS GREASES AND SEALING FLUIDS 1 2 GOOD WORKING PRACTICES 1 3 DISASSEMBLY AND ASSEMBLY 1 4 SPECIAL TOOLS 1 5 MEASURING 1 5 REMOVING AND INSTALLING 1 7 FEATURES AND BENEFITS 1 8 POWER UNIT 1 8 IGNITION SYSTEM 1 9 IGNITION TIMING IN NEUTRAL 1 10 COOLING SYSTEM 1 11 TILLER HANDLE 1 13 BRACKET AND BOTTOM COWLING 1 14 TECHNICAL TIPS 1 15 CARBURETOR 1 15 IGNITION SYSTEM 1 18 ...

Page 2: ...utboard motor s serial number is stamped is bonded to the port clamp bracket The label is specially treated so that peeling it off causes cracks across the serial number 1 Model name 2 Approval model code 3 Transom height 4 Serial number STARTING SERIAL NUMBERS The starting serial number blocks are as fol lows Model name Approval model code Starting serial number Worldwide 25BMH 61R S 020101 L 350...

Page 3: ...etroleum vapor is heavier than air and is deadly if inhaled in large quantities Engine exhaust gases are harmful to breathe When test running an engine indoors maintain good ventilation SELF PROTECTION Protect your eyes with suitable safety glasses or safety goggles when grinding or when doing any operation which may cause particles to fly off Protect hands and feet by wearing safety gloves or pro...

Page 4: ...soiled wiping rag in your pocket 4 Hands and any other part of the body which have been in contact with lubri cants or lubricant contaminated cloth ing should be thoroughly washed with hot water and soap as soon as practica ble 5 To protect the skin the application of a suitable barrier cream to the hands before working is recommended 6 A supply of clean lint free cloths should be available for wi...

Page 5: ...arts with compressed air when disassembling 2 Oil the contact surfaces of moving parts before assembly 3 After assembly check that moving parts operate normally 4 Install bearings with the manufacturer s markings on the side exposed to view and liberally oil the bearings 5 When installing oil seals apply a light coating of water resistant grease to the outside diameter ...

Page 6: ...N 90890 01252 2 Crank stand alignment P N 90890 03107 3 Pocket tester P N 90890 03112 4 Timing light P N 90890 03141 5 Compression Gauge P N 90890 03160 6 Peak voltage adaptor P N 90890 03172 7 Digital circuit tester P N 90890 03174 8 Ignition tester P N 90890 06754 9 Vacuum pressure pump gauge set P N 90890 06756 10 Digital tachometer P N 90890 06760 11 Leakage tester P N 90890 06762 12 Digital c...

Page 7: ...3006 P N 90890 03008 15 Inside micrometer P N 90890 03010 16 Thickness gauge P N 90890 03079 17 Shimming plate P N 90890 06701 18 Pinion height gauge P N 90890 06702 19 Magnet base P N 90890 06705 20 Backlash indicator P N 90890 06706 21 Magnet base plate P N 90890 07003 13 14 15 16 17 18 19 20 21 ...

Page 8: ... y P N 90890 06535 10 Stopper guide stand P N 90890 06538 11 Driver rod LL P N 90890 06605 12 Driver rod LS P N 90890 06606 13 Driver rod L3 P N 90890 06652 14 Driver rod SL P N 90890 06602 15 Driver rod SS P N 90890 06604 16 Bearing depth plate P N 90890 06603 17 Needle bearing attachment P N 90890 06608 P N 90890 06611 P N 90890 06615 18 Ball bearing attachment P N 90890 06633 19 Bearing inner r...

Page 9: ...previous 25V and 30G with newly designed linkage that controls both throttle opening and ignition timing mechanically and simultaneously Special attention was paid on the crankshaft bearings Collar is added to the upper main journal of the crankshaft Roller bearing is applied to the center bearing The collar added on the upper main journal contributes to get better serviceability Fig 2 Fig 1 ...

Page 10: ...oil Similar to the previous 25V and 30G the engine has the mechanical ignition timing advance system that works by way of the linkage Superior fuel economy is attained by the modified ignition timing control arrangement Also the system restricts the ignition timing advance when the shift is in neutral which helps to prevent the kickback at the engine start Fig 3 ...

Page 11: ...ight until it touches the Arm and ignition timing advance is stopped at the point A The Arm moves to the right or to the left when the shift is engaged since it is interlocked with the shift lever Thus when the shift is engaged the Lever does not touch the Arm at the point A allowing ignition timing advance to take place Fig 5 a b b a b Fig 4 ...

Page 12: ... structure applied to the cooling system provides additional cooling capacity in the upper casing With additional cooling water passage indicated by water walls contained in the new upper casing contribute to the reduction of outer surface temperature Fig 6 ...

Page 13: ...FEATURES AND BENEFITS GEN INFO 1 12 E COOLING SYSTEM Fig 7 ...

Page 14: ...pen positions Also new steering handle parts were developed to assume the long use Inner diameter of the steering handle engagement area and both inner and outer diameters of steering bracket are increased Please note that if the new steering handle is installed on the previous models Steering handle 2 Steering bracket Collar and Washer must be replaced Fig 9 100 degrees 90 degrees Fig 8 ...

Page 15: ...ES AND BENEFITS GEN INFO 1 14 E BRACKET AND BOTTOM COWLING The Bracket 1 is modified on the 25B and 30H and newly designed rubber seal is added to provide better sealing ability for the bottom cowling Fig 10 ...

Page 16: ...through the main nozzle At idling the fuel delivered from the pilot jet is mixed with the air delivered from the pilot air jet Air and fuel mixed at the rate determined by the pilot screw adjustment are supplied to the engine through the pilot outlet located above the throttle valve Once the throttle valve is opened to go beyond the bypass holes during the slow speed operation air fuel mixture is ...

Page 17: ...throttle valve opens in the mid speed range air fuel mixture is fed through the bypass holes in addition to the delivery through the pilot outlet Air fuel mixture is also delivered through the main nozzle depending on the throttle valve opening Fig 12 ...

Page 18: ...ottle valve is fully open the fuel delivered through the main jet is mixed with the air delivered through the main air jet which is fed into the venturi through the main nozzle Air fuel mixture delivery through the bypass holes and the pilot outlet continues in the high engine speed Fig 13 ...

Page 19: ...nd the pulser coil slides in accordance with the throttle valve opening Mechanical ignition timing advance applied in this system makes it easier to adjust and confirm the appropriate ignition timing In addition the ignition timing advance is restricted when the shift is in neutral which helps to prevent the kickback at the engine start Fig 15 Fig 14 ...

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