Mercury 25 BigFoot FourStroke Service Manual 90-854785R2 – 2002 25HP 4-Stroke Outboard Repair

Description

Mercury 25 BigFoot FourStroke Service Manual 90-854785R2

This is the complete service and repair manual for the Mercury 25 BigFoot FourStroke outboard, published by the Service Department of Mercury Marine under document number 90-854785R2 and dated December 2001. It is written for dealer mechanics and company service personnel servicing the 25 HP 4-stroke outboard, and it lays out every major system of the engine in dedicated sections with specifications, procedures, exploded views, and diagnostic references.

File Details

• Manual type: Service / Repair Manual
• Brand: Mercury Marine
• Model: 25 BigFoot FourStroke (25 HP, 4-stroke)
• Document number: 90-854785R2
• Edition / date: December 2001
• Language: English
• File format: PDF
• Page count: Approx. 471 pages

Chapters Covered

The manual is organised into nine top-level sections, each subdivided into the individual systems that make up the 25 BigFoot FourStroke. The Mercury 25 BigFoot FourStroke service manual covers:

• Section 1 — Important Information
  • A — Specifications
  • B — Maintenance
  • C — General Information
  • D — Outboard Motor Installation
• Section 2 — Electrical
  • A — Ignition
  • B — Charging & Starting System
  • C — Timing, Synchronizing & Adjusting
  • D — Wiring Diagrams
• Section 3 — Fuel System
  • A — Fuel Pump
  • B — Carburetor
  • C — Emissions
• Section 4 — Powerhead
  • A — Cylinder Head
  • B — Cylinder Block / Crankcase
  • C — Lubrication
• Section 5 — Mid-Section
  • A — Clamp/Swivel Brackets & Driveshaft Housing
  • B — Power Trim
  • C — Gas Assist Manual Tilt
• Section 6 — Lower Unit
  • Gear housing (driveshaft and propeller shaft)
  • Water pump, seals, bearings, clutch, and gear inspection
  • Pressure testing and gear housing installation
• Section 7 — Attachments / Control Linkage
  • A — Throttle / Shift Linkage
  • B — Tiller Handle
• Section 8 — Manual Starter
  • Recoil starter disassembly, rewind spring tension, and interlock cable adjustment
• Section 9 — Color Diagrams
  • Remote control electric, tiller handle electric, gas assist, and manual start wiring diagrams
  • Oil flow diagram and water flow diagram

Across these sections the Mercury 25 BigFoot FourStroke repair manual gives a technician the full scope of the 4-stroke 25 HP outboard: ignition, charging and starting circuits with resistance and DVA test values, fuel pump and carburetor servicing with jet sizes and float height, cylinder head and valve service, cylinder block and crankcase assembly with torque sequences, lubrication system clearances, power trim hydraulics with flow diagrams, gear housing disassembly and reassembly with bearing and seal procedures, throttle and shift cable adjustment, tiller handle servicing, and recoil starter repair.

Specifications & Reference Data Included

Beyond procedures, the Mercury 25 BigFoot FourStroke service manual carries the reference values needed to complete the work correctly. These include:

• Engine performance data — 25 HP (18.6 kW) at 5750 RPM, full throttle range 5500–6000 RPM, displacement 30.4 cu. in. (498 cc), compression ratio 9.8:1, firing order 1-2.
• Ignition data — NGK DPR6EA-9 spark plug, 0.035 in. (1.0 mm) gap, 150 lb-in. (17 Nm) torque, capacitor discharge ignition with ECM-controlled timing, charge coil and crank position sensor resistance values.
• Charging system data — 6 AMP manual alternator and 15 AMP electric alternator outputs with stator and battery charge coil resistances.
• Fuel system data — fuel pump pressure 3–6 PSI, plunger stroke 0.23–0.38 in., carburetor main/pilot/idle jet sizes for standard and Bodensee models, float height 0.47–0.63 in. (12.0–16.0 mm).
• Lubrication data — engine oil capacity either 3 quarts or 3 liters, oil pressure 30–40 PSI at 3000 RPM warm, oil pump clearances.
• Torque specifications — an extensive table covering electrical, fuel, mid-section, adaptor plate, steering arm, power trim, and lower unit fasteners.
• Gear housing data — 2.42:1 gear ratio, 14.9 fl. oz. (440 mL) capacity, 29-tooth forward gear, 12-tooth pinion, water pressure at idle and WOT.
• Mid-section data — transom heights, steering pivot range, tilt pin positions, full tilt up angle, allowable transom thickness.
• Propeller selection chart with diameter, pitch, blade count, material, boat weight, boat length, and Mercury part number.
• Mercury/Quicksilver lubricants and sealants list with part numbers.
• Cylinder head, valve, piston, ring, crankshaft, camshaft, and thermostat service limits.

Diagnostic Coverage

Diagnostics are a significant part of this 25 BigFoot FourStroke workshop manual. The ignition section includes a full troubleshooting table organised by symptom — no spark on both cylinders, no spark on one cylinder, weak spark, timing that will not advance, engine misfire at high RPM, hard starting cold and hot, engine not running over 2000 RPM, and engine surging over 6200 RPM — with probable causes and recommended test numbers. The charging system troubleshooting covers battery condition, stator ohm tests, regulator/rectifier diode and SCR tests for both analog and digital meters, and the starter circuit is presented as a step-by-step flow chart with test points identified on a diagram. Power trim hydraulic troubleshooting is broken into two flow charts — outboard not holding tilted position, and trim system leaking down with manual release valve closed. An electrical troubleshooting table for the power trim system isolates switch, relay, fuse, and motor faults by symptom.

Diagrams, Illustrations, and Wiring

The Mercury 25 BigFoot FourStroke repair manual is heavily illustrated. The powerhead is shown in front, starboard, port, top, and aft views with every hose, sensor, fitting, and connector identified. Exploded parts drawings accompany the fuel pump, carburetor, intake, cylinder head, camshaft, oil pump, power trim, gear housing, propeller shaft, tiller handle, and manual starter procedures. Wiring diagrams are provided for remote control electric, tiller handle electric, remote control electric with gas assist, and tiller handle manual configurations, with a dedicated color diagrams section for 2002 model year engines. Power trim flow diagrams show trim up, tilt up, maximum tilt, trim down, shock function up, shock function return, and manual tilt. Oil flow and water flow diagrams close out the manual.

What This Manual Lets You Do

With the Mercury 25 BigFoot FourStroke service manual 90-854785R2 on hand, a technician or owner can carry out the full range of repair and maintenance work on this specific 4-stroke 25 HP outboard. That includes ignition system testing and component replacement, charging and starting system diagnosis, timing belt and stator service, fuel pump and carburetor overhaul with correct jetting, cylinder head removal and valve adjustment, powerhead disassembly with piston and crankshaft inspection, lubrication system service, power trim hydraulic repair and pressure testing, lower unit disassembly with bearing and seal replacement, propeller shaft and clutch service, shift and throttle cable adjustment, tiller handle repair, and manual starter rewind servicing.

What matters is that the values are the right ones. A 4-stroke outboard is unforgiving of wrong clearances, wrong torque, and wrong jetting — the difference between a clean-running engine and a damaged one often comes down to a single specification. The Mercury 25 BigFoot FourStroke service manual supplies the factory specifications, the torque sequences, the clearances, and the resistance values that the job requires, along with the exploded views and wiring diagrams that show how the parts actually go together.

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The file is delivered as an instant PDF download — no shipping, no waiting. It opens on any device, can be printed for the workshop bench, and the pages you use most can be kept to hand while you work.