1998 Mercury Mariner 20 JET, 20, 25, 25 MARATHON and 25 SEAPRO Outboard Motor Service Manual (P/N 90-826883R2)

Mercury Marine service manual 90-826883R2, dated June 1998, covers the 1994–1999 Mercury/Mariner 20 JET, 20, 25, 25 MARATHON, and 25 SEAPRO two-stroke outboards within the serial ranges listed above.

Text search and wiring detail: The PDF has searchable text and embedded bookmarks for its sections and procedures. Some labels within older wiring drawings are outside the searchable text layer. Small wire-color codes and connector numbers require zooming for comfortable reading.

• Powerhead repair: Powerhead removal and reassembly, crankshaft and piston inspection, bearing and seal replacement, reed-block checks, and cylinder-bore repair limits.

• Fuel system: Carburetor removal and adjustment, fuel-pump rebuilding, primer-system diagnosis, float-level checks, and high-altitude jet charts.

• Ignition and electrical: Electronic and mechanical spark-advance diagnostics, BLACK- and RED-stator tests, charging-system checks, starter-motor repair, and wiring diagrams.

• Lower unit and jet drive: Gearcase disassembly, propeller-shaft and bearing-carrier service, jet-pump repair, liner replacement, and impeller-clearance adjustment.

• Cooling and maintenance: Water-pump impeller replacement, thermostat testing, cooling-system flushing, fuel-line inspection, corrosion-anode replacement, and storage preparation.

• Controls and manual starter: Tiller-handle and side-shift servicing, throttle/shift linkage adjustment, neutral-interlock checks, recoil-starter overhaul, and starter-rope replacement.

Written for dealer mechanics and Mercury Marine service personnel, this manual assumes familiarity with outboard servicing and the specified standard and special tools.

Powerhead Repair and Cylinder-Bore Differences

The powerhead section covers internal inspection through reassembly and test running. Factory torque specifications, fluid-capacity tables, wear limits, and adjustment data accompany the service material; illustrated torque sequences cover the exhaust, crankcase, and cylinder-block covers.

Chrome versus Mercosil: U.S. serial numbers through 0G202749 have chrome bores; 0G202750 and above use Mercosil. The manual separates their inspection and machining limits: chrome bores are not reboreable, while Mercosil blocks have an oversize repair provision.

Piston installation drawings identify orientation errors that can let the rings catch in the ports and damage the powerhead. The procedures specify tools including Piston Pin Tool 91-76160A2.

Reed-block inspection and bleed-hose routing are documented separately. A damaged reed-block component calls for replacement of the complete assembly; the manual does not treat individual reed components as separately supplied repair parts.

Ignition, Charging and Starting Diagnostics

Serial-specific stator, switch-box, and linkage tables help match the installed ignition system to the correct tests before parts are selected. The electronic-to-mechanical advance change occurs at U.S. serial 0G438000 for 20/25 models and 0G760300 for 20 JET models.

Diagnostic material includes the Electronic Spark Advance graph, Starting Circuit Troubleshooting Flow Chart, rectifier tests, and Commander remote-control wiring diagrams. Separate DVA and resistance tables cover the ignition configurations, with Multimeter/DVA Tester 91-99750A1 identified in the test procedures.

Timing and synchronization instructions distinguish tiller-handle, side-shift, and remote-control arrangements. Electrical reference data includes spark-plug gaps, stator winding readings, and ignition-coil test specifications.

Carburetor, Fuel Pump and Cooling Service

WMC carburetor tables distinguish standard and SeaPro/Marathon configurations. Troubleshooting charts address hard starting, flooding, surging, poor acceleration, and rich or lean running; the primer section links starting and idle symptoms to its diaphragm, check ball, and passages.

The cooling material includes thermostat opening tests and water-pump assembly views. It warns that reversing the established vane set of a reused impeller can cause the vanes to break. Maintenance schedules also address the extra flushing and corrosion checks needed after salt-water use.

Propeller Gearcase and Jet-Pump Variants

Gearcase service covers gears, clutch, shafts, bearings, seals, and leakage testing. The shared chapter also contains 9.9/15 Bigfoot four-stroke lower-unit procedures and a separate 2.42:1 specification table; these are distinct from the 2.25:1 20/25 master specifications and do not provide full Bigfoot engine coverage.

Jet-pump and linkage drawings split at U.S. serial 0G157845/0G157846. The jet section adds reverse-gate adjustment, cavitation checks, worn-impeller assessment, and installation details for small- and large-diameter single-bearing systems.

Midsection, Controls and Recoil Starter

Exploded views and torque tables identify clamp-bracket, swivel-bracket, and drive-shaft-housing components. Control sections cover cable routing and adjustment, throttle cams, horizontal shift shafts, and neutral interlocks; recoil-starter procedures include spring inspection and reassembly.

Marine fuel and electrical work carries fire and shock risks. Follow the manual’s precautions and consult a certified marine technician before major service work.

English PDF and Included Pages

Supplied as one printable, English-language 337-page PDF, including the original cover, three introductory pages, and one Notes page. These five pages are already included in the total.