The 1987 Yamaha 40 HP Outboard is a two-stroke marine engine featuring 40 horsepower output, electric start, remote control capability, 2-cylinder configuration, oil injection system, CD ignition, thermostatic cooling, and corrosion-resistant construction. This service manual provides comprehensive information for maintenance, troubleshooting, repair procedures, and specifications for the 1987 model year. Below are key sections covering safety, technical specifications, maintenance procedures, troubleshooting, and repair guidelines.
Essential safety guidelines for working on the Yamaha 40 HP outboard engine.
| Hazard | Precaution |
|---|---|
| Fuel and fire | Work in well-ventilated area; no smoking or open flames |
| Electrical shock | Disconnect battery before servicing electrical components |
| Moving parts | Remove spark plug wires when testing compression or rotating engine |
| Hot surfaces | Allow engine to cool before performing maintenance |
| Battery acid | Wear protective gloves and eyewear when handling batteries |
| Propeller | Remove propeller when working on lower unit |
Regular maintenance intervals for optimal performance and longevity.
WARNING! Always use Yamaha-approved lubricants and replacement parts.
Carburetor specifications and fuel system maintenance procedures.
| Component | Specification |
|---|---|
| Carburetor Type | Dual Mikuni BN38-48 |
| Main Jet Size | #115 |
| Pilot Jet Size | #40 |
| Float Level | 21.5mm |
| Fuel Pump Pressure | 2.5-3.5 psi |
| Oil Injection Ratio | 50:1 at wide open throttle |
Cleaning Procedure: Disassemble carburetors, clean with carburetor cleaner, blow out passages with compressed air, reassemble with new gaskets.
CD ignition system specifications and testing procedures.
Testing: Use multimeter to check coil resistances; replace if outside specifications.
Thermostatic cooling system maintenance and troubleshooting.
CAUTION! Never run engine without water supply to prevent impeller damage.
Gearcase service and propeller specifications.
| Component | Specification |
|---|---|
| Gearcase Oil Capacity | 300ml |
| Oil Type | Yamaha Gearcase Oil or equivalent 80W-90 |
| Propeller Diameter | 10-11 inches |
| Propeller Pitch | 11-15 inches |
| Shift Rod Height | 26.5mm from gearcase surface |
Inspection: Check for fishing line around propeller shaft, inspect seals for leaks.
Charging system and electrical component specifications.
Testing: Check charging voltage at battery with engine at 3000 RPM.
| Symptom | Possible Cause | Corrective Action |
|---|---|---|
| Engine won't start | Fuel, spark, or compression issue | Check fuel delivery, spark plugs, compression test |
| Overheating | Water pump, thermostat, blockage | Replace impeller, test thermostat, clear water passages |
| Poor performance | Carburetion, ignition timing | Clean carbs, check timing, compression test |
| No charging | Stator, rectifier, wiring | Test stator output, check rectifier diodes |
| Gearcase noise | Worn gears, bearings, improper oil | Inspect gears and bearings, change oil |
Critical fastener torque values for proper assembly.
| Component | Torque Value |
|---|---|
| Cylinder Head Bolts | 20-22 Nm (14-16 ft-lbs) |
| Spark Plugs | 25-30 Nm (18-22 ft-lbs) |
| Flywheel Nut | 60-70 Nm (44-52 ft-lbs) |
| Propeller Nut | 45-55 Nm (33-41 ft-lbs) |
| Gearcase Drain/Fill Screws | 8-12 Nm (6-9 ft-lbs) |
| Lower Unit Mounting Bolts | 25-30 Nm (18-22 ft-lbs) |
Complete electrical schematics for the 1987 Yamaha 40 HP outboard.
Main Harness: Color-coded wiring with connector locations and pin assignments.
Ignition Circuit: CDI unit, charge coils, pulsar coils, spark plugs.
Charging System: Stator, rectifier/regulator, battery connections.
Control Circuit: Start switch, stop switch, neutral safety switch.
Note: Refer to detailed wiring diagrams in the printed manual for specific wire colors and routing.