Yamaha 1984-87 25 HP Outboard Specs & Maintenance
Built between 1984 and 1987, this classic 25 HP 2-cylinder inline 2-stroke outboard is a legendary workhorse for aluminum fishing boats and light skiffs. Pushing a bulletproof 30 cubic inch (496 cc) displacement, it offers an incredible power-to-weight ratio that DIY mechanics love. Whether you’re restoring a mid-80s gem or performing routine service, our technical database provides the exact specs, spark plug gaps, and maintenance data needed to keep your motor running strong.
Complete Technical Specifications
| Specification | Details |
|---|---|
| Model / Horsepower | 25 |
| Year Range | 1984-87 |
| Engine Type | IL 2-stroke |
| Cylinders | 2 |
| Displacement | 30 cu-in (496 cc) |
| Bore x Stroke | 2.83 x 2.40 in (72 x 61 mm) |
| Compression Ratio | 7.0:1 |
| Full Throttle RPM | 4500-5500 |
| Idle Speed (Neutral) RPM | 850-950 |
| Idle Speed (Trolling) RPM | 750-850 |
| 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) | — |
| Ignition Timing (Carb Pickup) | — |
| Ignition Timing (Full Advance) | 24-26 |
| Fuel System | Carb |
| Starting System | Man or Man & Elec |
| Oil Injection System | Pre-Mix 100:1 |
| Injection Oil Ratio | Pre-Mix 100:1 |
| Gear Oil Capacity (mL/cc) | 180 |
| Gear Oil Capacity (Oz) | 6.1 |
| Approximate Weight | 114-127 lbs (52-58 kg) |
| Battery CCA / Reserve | 210 (40) |
| Battery Reserve | 59 minutes |
| Tach Pole Setting | 4 |
| Test Propeller Part Number | YB-1621 |
| Test Propeller New Engine RPM | 4200-4400 |
Maintenance Summary
Keep this 2-stroke running smoothly by inspecting the cooling impeller annually and mixing fresh fuel accurately. Always run NGK B7HS-10 spark plugs gapped to 0.035–0.039 inches (0.9–1.0 mm). Regular lower unit gear lube changes will ensure this tough 496 cc engine provides reliable seasons on the water.
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Notice: Specifications, fuel ratios, and maintenance guidelines listed on VintageMotorSpecs.com are compiled for historical reference and educational purposes only.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.
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