2005 KYMCO MXU 300 / MXU 250 Service Manual (PN 4121-LCA5/LDE9-S00)

• Coverage and document identity: 351-page PDF for the KYMCO MXU 250 model LB50 and MXU 300 model LA60, using the manufacturer’s April 2005 first-edition service information. The manual also separates on-road and off-road electrical configurations. Document code: 4121-LCA5/LDE9-S00.
• Engine repair procedures: Covers model-specific engine removal and installation, cylinder-head and camshaft service, rocker arms and valves, cylinder and piston inspection, oil-pump work, crankcase separation, crankshaft inspection, and balance-shaft timing.
• CVT and transmission service: Details drive and driven pulley disassembly, V-belt and clutch inspection, weight rollers, bushings, driven-face bearings, shift shafts, shift cams, shift forks, gears, dogs, bearings, oil seals, and reassembly checks.
• Different rear-drive systems are handled separately: MXU 250 chain drive, rear axle, axle hub, swingarm, and chain-slack adjustment; MXU 300 universal-joint and shaft drive, bevel-gear assemblies, rear final gear case, backlash, tooth-contact, and shim-selection procedures.
• Chassis and hydraulic repair coverage: Includes front and rear brake fluid replacement and bleeding, master-cylinder and caliper overhaul, wheel and hub service, front suspension, tie rods, steering column, toe-in adjustment, rear shock, axle, and swingarm work.
• Fuel, cooling, and electrical diagnosis: Covers the fuel tank and valve, PTG carburetor, PAIR system, cooling-system pressure testing and air bleeding, water-pump mechanical seal, battery and charging system, ignition controls, electric starter, starter clutch, and recoil starter.
• Reference material for the job: Supplies four configuration-specific full wiring diagrams, charging/ignition/starting circuit views, cable-and-harness routing illustrations, troubleshooting charts, bevel-gear contact and shim charts, torque tables, capacities, wear limits, electrical test values, and numbered special tools.

Coverage That Matches the Hardware

This is not a single set of generic instructions with “250/300” added to the page header. The MXU 250 is identified as the 249 cc LB50 configuration, while the MXU 300 is the 270 cc LA60. Both use a liquid-cooled OHC single-cylinder engine, carburetor, automatic V-belt drive, and electric/recoil starting, but their driveline repair paths differ in important ways.

The MXU 250 transmission can be serviced with the engine in the frame and feeds a chain-driven rear axle. Its sections cover the drive sprocket, main and counter axles, shift mechanism, axle hub, driven sprocket, chain adjustment, and MXU 250 swingarm. The MXU 300 transmission requires engine removal and continues through a secondary bevel-gear assembly, universal joint, rear driving mechanism, and final gear case. Those chapters include bearing and oil-seal replacement, shim selection, backlash measurement, and tooth-contact evaluation—critical information when the final drive has been opened or major parts have been replaced.

Workshop-Level Repair and Diagnosis

Engine coverage goes well beyond periodic service. The manual documents top-end disassembly and inspection, cam timing, valve-train repair, piston and ring inspection, cylinder measurement, crankcase separation, crankshaft and connecting-rod checks, and balance-shaft alignment. The CVT chapter supports belt, clutch, pulley, roller, spring, bushing, oil-seal, and bearing repair, with service limits and component-specific torque data.

Fuel and cooling sections cover throttle-valve work, carburetor disassembly and float inspection, air-cleaner housing, PAIR solenoid valve, radiator and cap testing, fan and thermostatic-switch checks, coolant replacement and air bleeding, thermostat and thermosensor testing, and water-pump mechanical-seal replacement. Brake chapters include both hand-control and pedal circuits, not just pad replacement.

Electrical fault finding is supported by no-start, low-power, poor-charging, and no-spark troubleshooting charts. Diagram coverage includes the MXU 250 and MXU 300 on-road/off-road wiring layouts, cable-and-harness routing views, the charging circuit, separate on-road and off-road ignition circuits, the starting circuit, and bevel-gear tooth-contact and shim charts.

Special Tools and Repair Cautions

The tool list identifies factory references such as the E003 flywheel puller, E012 tappet adjuster, E040 valve-spring compressor, E014 oil-seal and bearing installer, E017 universal holder, MXU 300 driveline tools F013/F014/F015, and the MXU 250 rear-axle nut wrench F010.

Two cautions show why the model-specific procedures matter. On the MXU 300, an incorrect final-drive shim can lock the gears while the case is being drawn together, so backlash and tooth contact are treated as a matched setup. In the CVT, grease or oil on the belt, pulley faces, or clutch linings can cause slipping and must be kept out of the friction surfaces.

Support the ATV and engine securely during removal work, isolate the battery before electrical repair, allow the cooling system to cool before opening it, and protect painted and plastic surfaces when servicing hydraulic brakes.