1986 Mercury 25 HP Outboard Manual

The 1986 Mercury 25 HP Outboard is a two-cylinder, two-stroke marine engine featuring 25 horsepower output, electric start capability, remote steering compatibility, 12-volt charging system, thermostatically controlled cooling, single carburetor, CD ignition system, and corrosion-resistant construction. Below are key sections for safety, specifications, operation, maintenance, troubleshooting, and service procedures.

1. Features at a Glance 2. Installation 3. First-Time Setup 4. Specifications 5. Controls and Operation 6. Maintenance Procedures 7. Fuel System 8. Electrical System 9. Storage & Winterization 10. Regulatory Information 11. Troubleshooting

Features at a Glance

Key components: Two-cylinder powerhead, CD ignition system, single carburetor, water pump cooling, electric start with manual backup, remote control compatibility.

Feature	Description
Power Output	25 horsepower at 5000-5500 RPM
Starting System	Electric start with manual recoil backup
Ignition System	CD (Capacitor Discharge) electronic ignition
Fuel System	Single barrel carburetor with fuel pump
Cooling System	Thermostatically controlled water pump
Gear Ratio	2.07:1 forward, neutral only
Propeller	3-blade aluminum, various pitches available
Weight	Approximately 105 lbs (47.6 kg)
Shaft Length	15-inch and 20-inch options
Charging System	6-amp alternator for battery charging

Installation

Proper mounting and setup procedures for optimal performance.

Select transom: Ensure transom height matches engine shaft length (15" or 20").
Mount engine: Use appropriate mounting bolts and transom clamps.
Connect steering: Install remote steering cables or tiller handle.
Connect fuel system: Attach fuel line with quick-connect fitting.
Connect battery: For electric start models, connect 12V battery with proper polarity.

WARNING! Engine is heavy; use proper lifting equipment. Ensure transom is structurally sound.

First-Time Setup

Initial preparation and break-in procedures.

Fuel mixture: Prepare 50:1 fuel/oil mixture (87 octane gasoline with TC-W3 oil).
Priming: Squeeze fuel line bulb until firm.
Starting: Set choke, turn key or pull starter cord.
Break-in period: Operate at varying speeds for first 10 hours.
Initial checks: Verify water pump discharge and oil injection (if equipped).

CAUTION! Always operate in well-ventilated area. Keep sparks and flames away from fuel.

Specifications

Displacement: 22.0 cubic inches (360 cc)
Bore x Stroke: 2.60" x 2.07" (66mm x 52.5mm)
Full Throttle RPM: 5000-5500 RPM
Fuel Capacity: 6-gallon remote tank standard
Fuel Consumption: Approx 2.5 gallons per hour at WOT
Oil Requirement: Mercury/Quicksilver TC-W3 2-stroke oil
Spark Plugs: Champion L77JC4 or equivalent, gap 0.030"
Gearcase Capacity: 11 oz (325 ml) 90-weight gear oil
Alternator Output: 6 amps at 5000 RPM

Controls and Operation

Understanding engine controls and proper operation procedures.

Tiller Handle: Throttle grip, gear shift lever, choke knob, stop button, tilt lock release.

Remote Control: Key switch, choke button, throttle/shift lever, trim switch, tachometer connection.

Starting Procedure: Set neutral, prime fuel, set choke, turn key/pull cord. Operation: Allow warm-up period, avoid prolonged trolling. Shutdown: Return to idle, turn off ignition, disconnect fuel if storing.

Maintenance Procedures

Scheduled maintenance for reliable operation.

Daily: Check fuel system for leaks, verify water pump discharge.
Monthly: Inspect spark plugs, check gear oil for water contamination.
100 hours/Annual: Replace water pump impeller, check thermostat.
300 hours: Decarbonize cylinders, inspect reed valves.
Storage: Fog cylinders, stabilize fuel, change gear oil.

Tip: Keep maintenance log for service intervals.

Fuel System

Fuel mixture requirements and carburetor maintenance.

Fuel mixture: 50:1 gasoline to TC-W3 oil ratio.
Carburetor adjustment: Idle mixture screw 1-1.5 turns out from lightly seated.
Fuel filter: Replace annually or if contaminated.
Fuel pump: Check diaphragm annually for cracks.
Fuel lines: Inspect for cracking or deterioration.

WARNING! Use only fresh gasoline. Stale fuel causes starting and performance issues.

Electrical System

Battery, charging, and ignition system maintenance.

Battery: 12V marine battery, minimum 450 CCA. Charging System: 6-amp alternator, check output annually. Ignition: CD unit sealed, no serviceable parts. Spark plugs: Replace every 100 hours or seasonally.

Storage & Winterization

Proper procedures for off-season storage.

Stabilize fuel: Add fuel stabilizer and run engine for 10 minutes.
Fog engine: Spray fogging oil into carburetor while running.
Change gear oil: Prevents water contamination damage.
Battery: Remove and store fully charged.
External: Flush with fresh water, lubricate linkages.

CAUTION! Store in dry location. Do not store with fuel in carburetor.

Regulatory Information

US Coast Guard certified. EPA emissions compliant for 1986 standards. Mercury Marine warranty: 1-year limited warranty from original purchase date. Copyright © 1986 Mercury Marine. For technical support, contact Mercury Marine Customer Service at 1-920-929-5040 or visit www.mercurymarine.com.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	Fuel, spark, or compression	Check fuel flow, spark plugs, compression; verify choke operation.
Overheating	Water pump, thermostat	Check water pump discharge; replace impeller if weak flow.
Poor performance	Fuel system, spark plugs	Clean carburetor, replace fuel filter, check spark plugs.
No charging	Alternator, rectifier	Test alternator output; check rectifier diodes.
Gear shifting issues	Linkage, cable adjustment	Adjust shift cable; check lower unit oil for metal particles.

Service: Authorized Mercury Marine dealers only for warranty work.

Parts: Genuine Mercury parts recommended for optimal performance.