Yamaha 1984-88 40 HP Outboard Specs & Maintenance
Known for its exceptional power-to-weight ratio and smooth operation, the 1984–1988 40 HP 3-cylinder 2-stroke outboard remains a favorite among vintage boating enthusiasts. Featuring a robust 43 cubic inch (698 cc) inline design, this triple-cylinder motor delivers reliable mid-range performance for aluminum fishing boats and light runabouts. Whether you’re restoring a classic or performing routine service, our technical database provides the exact specs to keep your motor running strong.
Complete Technical Specifications
| Specification | Details |
|---|---|
| Model / Horsepower | 40 |
| Year Range | 1984-88 |
| Engine Type | IL 2-stroke |
| Cylinders | 3 |
| Displacement | 43 cu-in (698 cc) |
| Bore x Stroke | 2.64 x 2.60 in (67 x 66 mm) |
| Compression Ratio | 6.0:1 |
| Full Throttle RPM | 4500-5500 |
| Idle Speed (Neutral) | 750-850 |
| Idle Speed (Trolling) | 550-650 |
| Spark Plug (NGK) | B7HS-10 |
| Spark Plug (Champion) | L82C |
| Spark Plug Gap | 0.035-0.039 in (0.9-1.0 mm) |
| Ignition System | CDI |
| Ignition Timing (Idle) | 4-6 ATDC |
| Ignition Timing (Carb Pickup) | 0-2 ATDC |
| Ignition Timing (Full Advance) | 24-26 |
| Fuel System | Carb |
| Starting System | Manual and/or Elec |
| Oil Injection System | PB or 50:1 PM |
| Injection Oil Ratio | PB or 50:1 PM |
| Gear Oil Capacity (mL/cc) | 430 |
| Gear Oil Capacity (Oz) | 14.5 |
| Approximate Weight | 149-198 (68-90) |
| Battery CCA / Reserve | 380 lbs (70 kg) |
| Battery Reserve | 124 minutes |
| Tach Pole Setting | 6 |
| Test Propeller Part Number | YB-1611 |
| Test Propeller New Engine RPM | 4900-5100 |
Maintenance Summary
Keep this 698 cc triple firing smoothly by inspecting fuel lines and maintaining precise ignition specs. Always run fresh 2-stroke fuel mix and install NGK B7HS-10 spark plugs set to a gap of 0.035–0.039 inches (0.9–1.0 mm) for optimal combustion and easy starting.
Disclaimer & Information Notice: Specifications, fuel ratios, and maintenance guidelines listed on VintageMotorSpecs.com are compiled for historical reference and educational purposes only. Always verify data against an official OEM service manual prior to ordering parts or executing repairs. VintageMotorSpecs.com assumes no liability for repair errors, equipment damage, or personal injury resulting from the use of this data.
Spot an error or discrepancy in these specs? Please contact us with your engine details so we can update our database.
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