Mercury Outboard Motors 70HP - 115HP Service Manual 1987-1993

Diagnostic procedures and component service for Mercury 70 HP, 75 HP, 80 HP, 90 HP, 100 HP, and 115 HP models (1987-1993). Includes diagnostic flowcharts. Ref: 90-13645-2

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Document Details

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Document Number / Seller:
31455 / Linda Davis
File Size:
8.74 MB
File Type:
PDF
Language:
English
Pages:
391
Printable:
Yes
Category:
Outboard Motor
Last updated / verified
Jul 1, 2025

Models Covered & Key Technical Specifications

Mercury 70 HP, 75 HP, 80 HP, 90 HP, 100 HP, 115 HP (90-13645--2) - 1987-1993

This is a comprehensive service manual covering Mercury outboard motors from 1987-1993.

  • Designated Capacity: The fuel tank capacity is 6.6 U.S. Gallons for all models listed.
  • Primary Specifications: Idle RPM is set between 650-700 in FORWARD gear across all listed models.
  • Advanced Testing Procedures: Ignition timing can be adjusted via the trigger assembly position for optimal performance.
  • Defined Compression Range: Cylinder bore is 3.375 inches (85.7mm) for 3-cylinder models and 3.375 inches (85.7mm) for 4-cylinder models.
  • Key Performance Metrics: Full Throttle RPM Range is 4750-5250 RPM for most models, with 100 and 115 HP models reaching 5000-5500 RPM.
  • Certified Lubrication: Engine weight varies from 260 lbs (ELO) to 360 lbs (ELOPT) depending on the specific model.

Professional Workshop Service Manual & Technical Specifications

Mercury 70 HP, 75 HP, 80 HP, 90 HP, 100 HP, 115 HP 1987-1993 - Comprehensive Outboard Service Manual Chassis-Documentation

Specification Rating Calibration-Data
Model Coverage 70, 75, 75 Marathon, 75XD, 75 Seapro, 80, 90 HP (1987-1993) and 100, 115 HP (4 Cylinder, 1988-1993) Serial Numbers provided for United States, Belgium, and Canada
Engine Type 3 Cylinder and 4 Cylinder, 2 Cycle N/A
Ignition Type C.D. Breakerless N/A
Fuel Type Regular Leaded, Premium, Low-Lead and Lead-Free automotive gasoline (86 octane minimum) N/A
Oil Type Quicksilver TC-WII or TC-W3 2-Cycle Outboard Oil N/A

Appropriately mandating precise engine maintenance, this manual details critical operational systems.

Maintenance hierarchies are structured into clear sections covering general information, electrical and ignition systems, fuel systems, oil injection, powerhead, and lower unit components.

Within the electrical and ignition sections, users will find in-depth coverage of stator tests, ignition coil diagnostics, and trigger adjustments. The fuel system chapters thoroughly document carburetor synchronization, fuel pump operation, and troubleshooting for various fuel-related issues.

The powerhead section provides detailed instructions for piston and ring installation, crankshaft procedures, and cylinder block maintenance. Lower unit service includes water pump repair, gear housing inspection, and propeller shaft reassembly. Torque specifications and special tools required for each procedure are clearly listed.

This manual documents torque specifications for critical engine components to ensure proper assembly and prevent structural misalignment prevention.

FAQ

Confirm the **recommended** diagnostic procedures for the ignition system? keyboard_arrow_down

Use a Multi-Meter/DVA Tester (91-99750) or a voltmeter capable of measuring 400 volts DC, or higher, with a Direct Voltage Adaptor (91-89045) for ignition system checks.

What tools **calibrated** fluid capacity requirements are specified? keyboard_arrow_down

6.6 U.S. Gallons (5 Imp. Gals.; 25 Liters) is the fuel tank capacity for all models.

Identify the **applicable** part number for the timing light? keyboard_arrow_down

91-99379 is the part number for the Timing Light, which may be obtained locally.

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Reviews (5)

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Rated 5 out of 5 stars
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I had a minor issue with my download link, but customer support responded in no time and resolved it. The manual itself is very comprehensive!
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This manual is a must-have! The troubleshooting guides helped me fix my engine quickly. The download was seamless and the support team was incredibly responsive.
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This manual has everything you need for maintaining your outboard. The parts diagrams are especially helpful. Quick download, too!
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I've used this manual for years. The detailed diagrams and service procedures are top-notch. Plus, the download process was super quick!