Do you have a question about the Yamaha YJ125S and is the answer not in the manual?
Details on identifying the scooter via VIN and model label.
Crucial information for maintenance, including preparation, parts, and seals.
Lists and illustrates special tools required for various maintenance and assembly tasks.
Detailed specifications for the engine, including type, displacement, bore, stroke, and oil/fuel requirements.
Specifications related to the scooter's frame, wheels, tires, and suspension systems.
Specifications for the electrical system components, including ignition, charging, and lighting.
Schedule for emission control system maintenance based on mileage and time intervals.
Schedule for general maintenance tasks and lubrication points based on mileage and time intervals.
Procedures for adjusting engine components like valve clearance and idling speed.
Step-by-step guide for flushing and replacing the brake fluid, including bleeding the system.
Procedure for checking tire pressure, tread depth, and wear limits, and condition.
Procedures for removing, checking, and installing the front wheel and brake disc.
Procedures for removing, checking, and adjusting the rear wheel and brake system.
Detailed information on front brake pads, master cylinder, and caliper maintenance.
Instructions for safely loosening and removing the front fork legs.
Inspection of inner/outer tubes, springs, damper rods, and other components for wear or damage.
Steps for assembling the front fork legs, including damper rod, spring, and seals.
Steps for removing the handlebar, switches, throttle grip, and master cylinder.
Inspection of the handlebar for bends, cracks, or damage.
Procedures for removing and installing the lower fender cover and handlebar holder.
Procedures for washing, checking, and replacing steering head bearings and races.
Steps for removing the rear shock absorber assembly, including covers and mounting hardware.
Inspection of the rear shock absorber rod, spring, bushings, and seals for wear or damage.
Exploded view and parts list for removing the cylinder head assembly.
Exploded view and parts list for removing rocker arms and camshaft.
Exploded view and parts list for removing valves and valve springs.
Procedures for removing, checking, and installing the cylinder, piston, and rings.
Steps for removing the V-belt drive components, including kickstarter and crankcase covers.
Procedures for removing and installing the kickstarter mechanism.
Exploded view and parts list for the V-belt, clutch, and sheave assembly.
Checking the oil pump driven gear and measuring internal clearances.
Steps for removing the transmission components, including oil drain and references to other sections.
Checking transmission gears, dogs, engagement, and movement for wear or damage.
Steps for removing the crankshaft assembly, timing chain, and guides.
Procedures for removing crankcase bolts and separating the crankcase halves.
Measuring crankshaft runout, width, and side clearance, and checking bearings and sprockets.
Exploded view and parts list for disassembling the carburetor.
Checking the carburetor body, float chamber, and float for cracks, dirt, or damage.
Procedure for measuring and adjusting the fuel level in the carburetor float chamber.
Steps for removing the air induction system components, including hoses and the air cut-off valve assembly.
Checking hoses and the air cut-off valve for cracks, damage, or proper continuity.
Detailed schematic illustrating the complete electrical system wiring, color codes, and component connections.
Covers the ignition system's circuit diagram and troubleshooting.
Details the electric starting system's circuit diagram, operation, and troubleshooting.
Covers the lighting system's circuit diagram, troubleshooting, and checks.
Procedures for checking the starter motor's commutator, mica undercut, and armature resistances.
Common causes and checks for engine starting failures.
Troubleshooting steps for incorrect engine idling speed.
Diagnosing issues related to poor performance and clutch malfunctions.
Troubleshooting common problems like overheating, poor braking, and faulty front forks.
Troubleshooting common lighting and signaling system malfunctions.
Diagnosing why the headlight fails to illuminate.
Diagnosing why the horn fails to produce sound.