Yamaha 1984-92 9.9 HP Outboard Specs & Maintenance
Produced between 1984 and 1992, this classic 9.9 HP two-stroke, twin-cylinder outboard is a legend among lightweight marine engines. Packing a durable 15 cubic inch (246 cc) displacement, it offers exceptional power-to-weight performance for aluminum fishing boats, skiffs, and tenders. Whether you are restoring a vintage runner or maintaining a reliable kicker, keeping this inline engine running smoothly requires proper tuning, routine fuel-system care, and precise ignition maintenance.
Complete Technical Specifications
| Specification | Details |
|---|---|
| Model / Horsepower | 9.9 |
| Year Range | 1984-92 |
| Engine Type | IL 2-stroke |
| Cylinders | 2 |
| Displacement | 15 cu-in (246 mm) |
| Bore x Stroke | 2.20 x 1.97 in (56 x 50 mm) |
| Compression Ratio | 7.0:1 |
| Full Throttle RPM | 4500-5500 |
| Idle Speed (Neutral) RPM | 850-950 |
| Idle Speed (Trolling) RPM | 670-770 |
| 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 |
| Ignition Timing (Carb Pickup) | 9-11 |
| Ignition Timing (Full Advance) | 29-31 |
| 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) | 185 |
| Gear Oil Capacity (Oz) | 6.3 |
| Approximate Weight | 83-87 lbs (38-40 kg) |
| Battery CCA / Reserve | 210 (40) |
| Battery Reserve | 59 minutes |
| Tach Pole Setting | 4 |
| Test Propeller Part Number | YB-1619 |
| Test Propeller New Engine RPM | 5000-5200 |
Maintenance Summary
Keep your 9.9 HP two-stroke running reliably with routine service. Always use correctly gapped NGK B7HS-10 spark plugs set to 0.035–0.039 inches (0.9–1.0 mm). Inspect lower unit gear lube, flush cooling passages regularly, and maintain fresh, properly mixed 2-stroke fuel to prevent carb fouling.
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Notice: Specifications, fuel ratios, and maintenance guidelines listed on VintageMotorSpecs.com are compiled for historical reference and educational purposes only.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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