1971 Mercury 9.8 HP Merc 110 Outboard Specs & Part Numbers
Technical Guide: 1971 Mercury 9.8 HP (Merc 110) Outboard Motor
The 1971 Mercury 9.8 HP, commonly designated as the Merc 110, is a classic twin-cylinder, two-stroke outboard motor engineered by Kiekhaefer Mercury. Known for its distinct “Phantom Black” styling, excellent power-to-weight ratio, and robust build quality, this motor remains a favorite among vintage outboard collectors and small-craft anglers. This technical guide provides comprehensive specifications, maintenance data, and historical context for restoring or servicing this iconic outboard.
Overview & Specifications
The Merc 110 is a loop-scavenged, twin-cylinder engine that shares its basic block design with other small displacement Mercury outboards of its era. It is highly valued for its lightweight portability and steady low-end torque.
| Specification | Value / Detail |
|---|---|
| Horsepower | 9.8 HP @ 5000–5500 RPM |
| Configuration | In-line 2-Cylinder, 2-Stroke |
| Displacement | 10.9 cubic inches (178.6 cc) |
| Bore x Stroke | 2.000 in. x 1.750 in. (50.8 mm x 44.45 mm) |
| Fuel-to-Oil Ratio | 50:1 (Unleaded 87 octane + TC-W3 outboard oil) |
| Cooling System | Water-cooled (direct-drive rubber impeller) |
| Dry Weight | ~65 lbs (29.5 kg) |
| Starting System | Manual recoil rope start |
| Gear Ratio | 2.0:1 |
Common Maintenance & Tune-up Specs
To keep the 1971 Merc 110 running smoothly, regular electrical, fuel system, and lower unit maintenance is required. Because this motor relies on a classic magneto ignition system, precise gapping is crucial for reliable starting and idle quality.
Ignition & Electrical System
- Spark Plug Type: NGK BP6HS or Champion L4J (some manuals also list NGK B6HS depending on running temperatures).
- Spark Plug Gap: 0.030 inches (0.76 mm).
- Ignition Type: Makerpoint Magneto system (utilizes dual sets of breaker points and condensers located under the flywheel).
- Breaker Point Gap: 0.020 inches (0.51 mm).
- Timing Adjustment: Static timing marks are located on the flywheel and magneto stator plate. Adjusting the point gap directly affects ignition timing.
Fuel & Carburetion
- Carburetor Model: Tillotson (typically KB-11A series or equivalent depending on production run).
- Low-Speed Idle Mixture Screw: Initial setting is 1 to 1-1/4 turns open from gently seated. Fine-tune with the engine running in Forward gear in a test tank.
- Fuel Pump: Integrated diaphragm-type fuel pump mounted directly to the side of the carburetor, actuated by crankcase pressure pulses.
Lower Unit & Gearcase
- Gearcase Lubricant: SAE 90 Hypoid Outboard Gear Lube (meeting API GL-5 specs or Mercury Premium Gear Lube).
- Capacity: Approximately 6 fl. oz. Fill from the bottom drain hole until fluid exits the upper vent hole to avoid trapping air pockets.
- Impeller Replacement: Water pump housing is located at the top of the lower gearcase unit on the driveshaft. Recommended replacement interval is every 2 seasons or if water flow from the “tell-tale” stream diminishes. (OEM Impeller Part Number: 47-89981-1 / modern equivalents).
Notable Features & History
The “Merc 110” Moniker
In the late 1960s and early 1970s, Kiekhaefer Mercury used a numbering system where the model number roughly corresponded to the horsepower rating multiplied by ten. Thus, the 9.8 HP model was badged as the Merc 110 (while the 7.5 HP was the Merc 75, and the 20 HP was the Merc 200). This marketing approach conveyed a sense of high performance and structural consistency across the lineup.
Thunderbolt Ignition Transition
While later 1970s Mercury outboards featured the revolutionary solid-state “Thunderbolt” CDI ignition systems, the 1971 Merc 110 utilized the highly reliable Kiekhaefer “Makerpoint” ignition. This was a hybrid step in Mercury’s engineering path, providing a hot, clean spark but still relying on mechanical breaker points that require periodic cleaning, alignment, and adjustment.
Key Design Features
- Under-Cowl Exhaust: Unlike many competitor outboards of the early 1970s that vented exhaust loudly into the upper column, the Merc 110 featured an underwater thru-hub exhaust system. This made the motor significantly quieter during operation and kept exhaust fumes out of the boat.
- F-N-R Shifting: Features a full Forward-Neutral-Reverse gearshift lever located on the starboard side of the engine cowl, providing excellent maneuverability compared to smaller direct-drive or pivot-reverse outboards of the same era.
- Corrosion Resistance: Engineered with “Kiekhaefer Mercury” specialty aluminum alloys and coated in high-gloss black acrylic enamel, these motors were highly resistant to harsh freshwater and saltwater environments, which explains why so many are still operational today.