Mercury 90-300 HP 2-Stroke Inline 6, V6 Repair Manual 1965-1989

SKU: SE1408

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Mercury 90-300 HP 2-Stroke Repair Manual 1965-1989
Mercury 90-300 HP 2-Stroke Repair Manual 1965-1989
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Item Description

This Seloc repair manual covers 1965-1989 Mercury Outboard 90-300 HP, inline 6 and V6, 2-stroke motors. Includes fuel-injection and MR drive.

Step-by-step illustrated keyed procedures guide you through every conceivable job possible, including all adjustments necessary. Perfect for do-it-yourselfers, professional mechanics, or students.

Book Excerpt: 1965-1989 Mercury 90-300 HP 2-Stroke Inline 6, V6 Repair Manual



If a problem is encountered with powerhead startup or operation, the determination must be made: the problem is in the ignition system or the fuel system is at fault.

The first and easiest test to determine an ignition problem is to perform a spark test as outlined in Chapter 5. If the ignition system checks out and the preliminary troubleshooting narrows the area to the fuel system, proceed with the following fuel system tests.


If troubleshooting should indicate the anti-siphon valve is at fault, attempt to operate the powerhead with a separate source of fuel. In other words, the valve is physically bypassed.

If the valve proves to be the source of the problem, either remove the valve from the fuel line or replace the valve with a solenoid operated fuel shutoff valve.


  1. Connect one end of a jumper cable to the terminal of the mercury switch and the other end to a suitable ground on the powerhead. The terminal will have a Black/Yellow lead attached to it.

    Grounding the mercury switch is necessary to prevent the powerhead from accidentally starting while test are being performed. Keep switch grounded with the jumper cable in place while performing Steps 2 thru 12, then remove the cable.

  2. Rotate the ignition key to the START position and crank the powerhead through several revolutions. Rotate the key switch back to the OFF position.

    Remove the spark plugs one by one and then inspect the electrode end. A damp electrode will indicate the injector is functioning for the cylinder being checked.

If all spark plugs are damp indicating the presence of fuel, all injectors are spraying fuel into the crankcase.

If some spark plugs are damp with fuel, while others are dry, the electric fuel pump is probably functioning correctly. However, either the injectors of the "dry" cylinders have a restricted fuel flow OR the dry injectors have an electrical problem.

If all spark plugs are dry andmdash; none are damp with fuel, a problem with fuel delivery exists. The problem may be:

  • A main fuel line blockage.
  • A faulty electrical component affecting operation of the entire system, such as a defective electric fuel pump, defective injector harness plug, or a component within the ECU.


The throttle control may be a remote control lever or a throttle twist grip. The control is always connected by linkage to the trigger assembly. When the throttle is advanced to increase powerhead rpm, the trigger coils are also advanced.

This arrangement provides advanced powerhead timing automatically as powerhead rpm increases.

The carburetor MUST provide additional fuel as powerhead rpm increases. The throttle plate shutter position in the carburetor bore determines the volume of air/fuel mixture supplied to the combustion chamber.

The throttle pickup adjustment is the preset point of spark advance when the throttle plate shutter BEGINS to open.

Subject: 1965, 1966, 1967, 1968, 1969, 1970, 1971, 1972, 1973, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989 Mercury 90-300 HP 2-Stroke Inline 6, V6 service, maintenance, repair. ISBN-10: 0893300144 | ISBN-13: 9780893300142 | Seloc 1408

  • Publisher: Seloc Publishing
  • Pages: 320 - Hundreds of b&w photos and illustrations
  • Binding: Paperback - 8.5 x 11 inches
  • ISBN: 978-0-89330-014-2
  • Years: 1965 - 1989
Table of Contents
  • General information
  • Tools and equipment
  • Boating safety
  • Engine tune-up
  • Engine disassembly and reassembly
  • Fuel system
  • Ignition system
  • Electrical system
  • Cooling system
  • Drive unit
  • Tilt and trim systems
  • Engine specs
  • Torque specs
  • Maintenance and off-season storage
  • Wiring diagrams
Questions & Answers about Mercury 90-300 HP 2-Stroke Repair Manual 1965-1989

Questions & Answers about Mercury 90-300 HP 2-Stroke Repair Manual 1965-1989

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Customer Reviews


Brian Miller verified customerMay 3, 2020
Great Book !
This is just the book I needed to restore my 1969 Mercury, had all the info I needed and was very easy to understand !
I know now wear to go for a great source of info in a Book !!!
Thank You !

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David verified customerApril 26, 2016
Great Manual
Manual was just as described and shipping was fast.
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Mercury 90-300 HP 2-Stroke Inline 6, V6 Repair Manual 1965-1989
Free Shipping (US48)
In Stock