1978 Evinrude 15 HP Fastwin Outboard Specs & Part Numbers
Introduction
The 1978 Evinrude 15 HP outboard motor is a legendary piece of marine engineering. Built during the golden era of Outboard Marine Corporation (OMC), this twin-cylinder, two-stroke motor is highly sought after today by fishermen, restoration enthusiasts, and boaters alike. Renowned for its lightweight design, exceptional power-to-weight ratio, and unmatched reliability, this motor represents the peak of OMC’s portable outboard design. Whether you are maintaining an original unit or embarking on a complete restoration, this technical guide provides the essential specifications, maintenance data, and historical context required to keep this classic motor running smoothly.
Overview & Technical Specifications
The 1978 Evinrude 15 HP (often affectionately grouped under the “Fastwin” lineage, though official badging during this specific late-70s era shifted simply to “Evinrude 15”) shares its block configuration with the equally famous 9.9 HP model of the same era. However, the 15 HP model utilizes a different carburetor throat diameter, different exhaust megaphone tuning, and altered porting configuration to achieve the additional horsepower from the same physical displacement.
| Specification | Value / Measurement |
|---|---|
| Horsepower | 15 HP @ 5500 RPM |
| Engine Type | 2-Stroke, Inline 2-Cylinder (Cross-flow scavenged) |
| Displacement | 13.2 cubic inches (216 cc) |
| Bore & Stroke | 2.25 inches x 1.66 inches (57.15 mm x 42.16 mm) |
| Fuel/Oil Ratio | 50:1 (Regular Unleaded 87 Octane + TC-W3 Marine Oil) |
| Starting System | Manual Recoil Starter (Electric start optional on some models) |
| Dry Weight | Approximately 74 lbs (33.5 kg) for short shaft models |
| Operating RPM Range | 5000 – 6000 RPM |
Common Maintenance & Tune-up Specs
To keep the 1978 Evinrude 15 HP running at peak efficiency, regular ignition, fuel, and cooling system maintenance is critical. Below are the precise technical tolerances and part specifications required for routine servicing.
Ignition & Electrical System
By 1978, OMC had transitioned this engine family to a solid-state Capacitor Discharge Ignition (CDI) system. This completely eliminated the mechanical breaker points used in earlier generations, drastically reducing ignition maintenance.
- Spark Plug Type: Champion L77JC4 (or QL77JC4 for suppression of radio/sonar interference)
- Spark Plug Gap: 0.030 inches (0.76 mm)
- Spark Plug Torque: 17.5 – 20.5 lb-ft
- Breaker Point Gap: N/A (Solid State CDI Ignition system / Power Pack – no mechanical points to gap)
- Ignition Timing: Set dynamically via the throttle linkage cam follower (ensure the roller aligns with the mark on the timing plate as the carburetor throttle plate begins to open).
Fuel & Carburetion
The fuel system requires clean, ethanol-free fuel whenever possible to protect the vintage elastomeric components inside the fuel pump and carburetor.
- Fuel Mixture: 50:1 ratio. This translates to 1 pint (16 oz) of high-quality TC-W3 2-stroke outboard oil to 6 U.S. gallons of gasoline.
- Low-Speed Idle Mixture Adjustment: Initial setting is 1.5 turns open from gently seated. Adjust clockwise to lean the idle mixture, and counter-clockwise to richen. Adjust in 1/8-turn increments with the engine warm and idling in forward gear.
- High-Speed Jet: Fixed orifice (No adjustment needle; if the engine runs lean at high speed, the jet must be physically cleaned or replaced).
Lower Unit & Cooling System
The water pump and lower unit gearcase are the lifelines of the engine. Neglecting these can result in catastrophic powerhead failure or gear damage.
- Water Pump Impeller Part Number: OEM OMC/BRP Part #395289 (Sierra Replacement Part #18-3051)
- Impeller Replacement Interval: Annually or every 100 hours of operation.
- Gearcase Lubricant: Marine SAE 80W-90 Outboard Gear Lubricant (Hi-Vis or equivalent)
- Gearcase Capacity: Approximately 9.0 fluid ounces (266 ml)
- Gearcase Refill Procedure: Always fill from the bottom drain hole until fluid exits the top vent plug hole to prevent trapping air pockets in the gear housing.
Notable Features & History
The 1978 Evinrude 15 HP is a hallmark of OMC’s engineering legacy, marking several milestones in the development of portable outboard motors.
The Legacy of the “Fastwin”
The name “Fastwin” was historically applied to Evinrude’s workhorse mid-range outboards starting in the 1950s. While official branding shifted in the late 1970s toward plain horsepower badging, the 1978 15 HP model inherited the pure DNA of the Fastwin lineage: a lightweight, twin-cylinder platform designed to be easily carried by hand but powerful enough to plane a 14-foot aluminum utility boat.
The 1974-1992 Engine Architecture
In 1974, OMC introduced a completely redesigned 9.9 / 15 HP platform. This specific design ran with minimal structural modifications all the way until 1992. The 1978 model year sits in the “sweet spot” of this run. It benefited from the early design refinements—such as the transition to the reliable, low-maintenance CDI “Power Pack” ignition system—while retaining the simple, lightweight, and durable mechanical construction that made the motor famous.
Key Design Features
- Shallow Water Drive: A manual tilt bracket system that allows the engine to be run at a elevated angle, protecting the lower unit when navigating shallow flats or rocky riverbeds.
- Vibration Isolation: The 1978 model features an innovative rubber-mount suspension system inside the swivel bracket, which isolates engine harmonics from the boat transom, delivering an exceptionally smooth, quiet ride compared to competitive motors of the era.
- Thru-Hub Exhaust: Unlike older outboards that discharged exhaust gasses above the propeller, the 1978 Evinrude discharges exhaust directly through the center of the propeller hub underwater. This design significantly reduces operating noise and improves engine breathing efficiency.
- Ease of Service: Parts availability for this engine family remains virtually unmatched. Because millions of these 9.9 HP and 15 HP OMC motors were produced over nearly two decades, OEM and aftermarket parts (such as carb kits, ignitions, water pumps, and gaskets) are cheap, abundant, and widely stocked worldwide today.