Yamaha 1988 25 HP Outboard Specs & Maintenance
The 1988 25 HP 2-stroke outboard remains a classic workhorse for fishing boats and lightweight runabouts alike. Powered by a bulletproof 2-cylinder, 395cc (24 cu in) inline engine, this vintage motor delivers exceptional power-to-weight performance and legendary reliability. Whether you’re restoring a mid-80s gem or performing routine maintenance, our comprehensive technical guide provides all the factory specifications, tuning tips, and hard-to-find part numbers needed to keep your classic 25 HP running smooth.
Complete Technical Specifications
| Specification | Details |
|---|---|
| Model / Horsepower | 25 |
| Year Range | 1988 |
| Engine Type | IL 2-stroke |
| Cylinders | 2 |
| Displacement | 24 cu-in (395 cc) |
| Bore x Stroke | 2.64 x 2.20 in (67 x 56 mm) |
| Compression Ratio | 7.0:1 |
| Full Throttle RPM | 5000-6000 |
| Idle Speed (Neutral) RPM | 700-800 |
| Idle Speed (Trolling) RPM | 600-700 |
| 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) | 2-4 ATDC |
| Ignition Timing (Full Advance) | 24-26 |
| Fuel System | Carb |
| Starting System | Man or Man & Elec |
| Oil Injection System | PB or 100:1 PM |
| Injection Oil Ratio | PB or 100:1 PM |
| Gear Oil Capacity (mL/cc) | 375 |
| Gear Oil Capacity (Oz) | 12.7 |
| Approximate Weight | 106-115 lbs (48-52 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-cylinder 2-stroke performing at its peak with consistent ignition care. Ensure proper spark by running NGK B7HS-10 plugs gapped precisely between 0.035 and 0.039 inches (0.9–1.0 mm). Regular fuel system maintenance and fresh gear lube will keep this 395cc motor reliable for years.
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Notice: Specifications, fuel ratios, and maintenance guidelines listed on VintageMotorSpecs.com are compiled for historical reference and educational purposes only.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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