Yamaha CV25 Outboard Motor Service Manual (P/N LIT-18616-00-55)

• Document and model coverage: A 130-page PDF of Yamaha's CV25 Service Manual, 1st Edition, April 1990, P/N LIT-18616-00-55. It covers the CV25ED remote-control and CV25EMD manual-control 25-hp outboards, both listed with electric and manual starting systems, beginning with serial block CV25 L:328669 and later.
• Predelivery and periodic service: Documents electrical and fuel-line checks, control operation, gear-oil service, leak and noise checks, idle speed, ignition timing, carburetor and throttle-link adjustment, start-in-gear protection, battery care, anode inspection, and propeller service.
• Fuel and powerhead repair: Covers the fuel tank and meter, priming pump, filter, diaphragm pump, and carburetor, followed by powerhead removal, disassembly, internal inspection, crank-cylinder assembly, cylinder-head and exhaust-cover installation, and recoil-starter repair.
• Lower-unit and bracket work: Provides gearcase removal and disassembly, internal component inspection, pinion and gear-shim selection, forward/reverse backlash adjustment, water-pump installation, leakage testing, reassembly, and service of the steering, clamp, rubber-mount, and tilt-lock assemblies.
• Electrical diagnosis: Supplies the CV25ED wiring diagram, CV25EMD wiring diagram, and 703 Remote Control Box schematic, along with component resistance and continuity checks, flywheel-magneto service, and starter-motor overhaul procedures.
• Illustrations, troubleshooting, and specifications: Exploded diagrams for the carburetor, power unit, and lower unit support parts identification. Symptom charts address no-start, rough idle, stalling, failure to stop, and hard or impossible shifting, while factory tables provide torque, clearance, wear-limit, adjustment, and electrical test data.

Model Identification and Workshop Level

Yamaha prepared this manual primarily for its dealers and trained mechanics, and the procedures assume a basic understanding of the mechanical and electrical work involved. The identification section shows the outboard serial plate on the port side of the clamp bracket and the separate engine number on the port side of the cylinder body, allowing the starting serial block to be checked before repair information or parts are selected.

Service and Overhaul Detail

The General Service chapter separates predelivery inspection from scheduled maintenance. Beyond routine checks, it covers ignition timing by dial gauge and timing light, carburetor control-link setup, throttle-link adjustment, and start-in-gear protection. Specifications appear with the related procedures and in dedicated tables for engine dimensions, carburetor settings, ignition components, starter-motor limits, mounting dimensions, and component-specific tightening torques.

Fuel-system repair is broken down by assembly rather than treated as a single tune-up topic. Inspection points cover the fuel-meter pickup and strainer, priming-pump check valves, filter, pump body, valves and diaphragm, carburetor passages, needle valve, float, pilot circuit, and leak-free hose installation. The manual specifically warns against cleaning carburetor jets with steel wire because enlarging the metering passages can seriously affect engine performance.

Powerhead coverage extends through removal, teardown, measurement, repair decisions, and final installation. Cylinder-head flatness, cylinder taper and out-of-round, piston and ring fit, crankshaft alignment and connecting-rod play, reed-valve condition, thermostat operation, and bearing condition are all addressed. Reassembly identifies bearing and oil-seal direction, piston orientation, ring locating pins, sealing-agent locations, staged fastener tightening, and the final free-rotation check. Installing the powerhead oil seal in the wrong direction is specifically identified as a damage risk.

Gearcase, Electrical, and Diagnostic Coverage

The lower-unit section explains when the original gearcase and internal parts can retain their shim setup and when replacement bearings, gears, or a gearcase require a new shim selection. It uses bearing models, pinion-position measurement, dial-gauge backlash checks, and forward/reverse shim-selection graphs before final gearcase assembly. The same chapter covers clutch-dog and gear inspection, driveshaft and propeller-shaft checks, impeller replacement, water-pump assembly, a lower-unit pressure leakage test, and shift-linkage setup.

Electrical repair distinguishes the CV25ED choke-solenoid arrangement from the CV25EMD engine-side starting- and stop-switch arrangement. Test procedures cover the pulser, charge, lighting, and ignition coils; CDI unit; starter relay; rectifier; fuse; switches; wiring harness; and battery. The starter-motor section carries the work through pinion and overrunning-clutch inspection, brush and commutator measurements, armature testing, reassembly, and installation. Yamaha tool numbers are supplied for equipment such as the YB-1621 test propeller, YB-6139 flywheel magneto holder assembly, YB-34232 pinion-gear shimming tool, and YB-6265 backlash indicator rod.

Fuel handling, battery service, ignition-timing checks, and work around the flywheel and propeller require the ventilation, fire-prevention, electrical-isolation, test-tank, and rotating-parts precautions stated in the manual.