Yamaha 1984-92 4 HP Outboard Specs & Maintenance
Built between 1984 and 1992, this lightweight 4 HP 2-stroke outboard motor remains a favorite among vintage marine enthusiasts and dinghy skippers alike. Powered by a dependable 5.0 cu in (83 cc) single-cylinder engine, this compact workhorse offers the perfect balance of portability and reliable performance. Whether you’re restoring a classic auxiliary motor or keeping your fishing skiff running smooth, our comprehensive database provides the vital specs and technical guidance you need.
Complete Technical Specifications
| Specification | Details |
|---|---|
| Model / Horsepower | 4 |
| Year Range | 1984-92 |
| Engine Type | CL 2-stroke |
| Cylinders | 1 |
| Displacement | 5.0 cu-in (83 cc) |
| Bore x Stroke | 1.97 x 1.65 in (50 x 42 mm) |
| Compression Ratio | 7.0:1 |
| Full Throttle RPM | 4500-5500 |
| Idle Speed (Neutral) RPM | 1100-1200 |
| Idle Speed (Trolling) RPM | 950-1050 |
| Spark Plug (NGK) | B7HS |
| Spark Plug (Champion) | L82C |
| Spark Plug Gap | 0.020-0.024 in (0.5-0.6 mm) |
| Ignition System | CDI |
| Ignition Timing (Idle) | 3-7 |
| Ignition Timing (Carb Pickup) | — |
| Ignition Timing (Full Advance) | 25-31 |
| Fuel System | Carb |
| Starting System | Manual |
| Oil Injection System | Pre-Mix 100:1 |
| Injection Oil Ratio | Pre-Mix 100:1 |
| Gear Oil Capacity (mL/cc) | 105 |
| Gear Oil Capacity (Oz) | 3.6 |
| Approximate Weight | 44-47 lbs (20-22 kg) |
| Battery CCA / Reserve | n/a |
| Battery Reserve | n/a |
| Tach Pole Setting | 4 |
| Test Propeller Part Number | — |
| Test Propeller New Engine RPM | — |
Maintenance Summary
Keep this 4 HP single-cylinder running at peak performance with routine ignition and fuel maintenance. Always use a properly gapped NGK B7HS spark plug set between 0.020 and 0.024 inches (0.5–0.6 mm). Fresh 2-stroke fuel mix and regular lower unit gear lube changes ensure smooth trolling all season long.
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Notice: Specifications, fuel ratios, and maintenance guidelines listed on VintageMotorSpecs.com are compiled for historical reference and educational purposes only.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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