Mariner 70 User manual

(3 Cylinder)
UNITED STATES S/N 0A996142 thru 0D283221
BELGIUM S/N 09502135 thru 09793576
CANADA S/N 0A722297 and Above BELGIUM CANADA
S/N 0B209468 thru 0D283221
S/N 09523034 thru 09793576
S/N 0A731673 and Above
MODELS
70 •75 •80 •90 •100 •115
SERVICE
MANUAL
1987–1993 70 •75 •75 Marathon •
75XD •75 Seapro •80 •90 1988–1993 100 •115 (4 Cylinder) with Serial Numbers
with Serial Numbers UNITED STATES
Printed in U.S.A. 1995, Brunswick Corporation 90-13645--2 1095

Notice
Throughout this publication, “Dangers”, “Warnings”
and “Cautions” (outlined in a border and accompa-
nied by the International HAZARD Symbol ) are
usedtoalertthemechanictospecialinstructionscon-
cerning a particular service or operation that may be
hazardous if performed incorrectly or carelessly.
OBSERVE THEM CAREFULLY!
These “Safety Alerts” alone cannot eliminate the
hazards that they signal. Strict compliance to these
specialinstructionswhenperformingtheservice,plus
“common sense” operation, are major accident
prevention measures.
DANGER
DANGER — Immediate hazards which WILL result
in severe personal injury or death.
WARNING
WARNING - Hazards or unsafe practices which
COULD result in severe personal injury or death.
CAUTION — Hazards or unsafe practices which
could result in minor personal injury or product or
property damage.
CAUTION
Notice to Users of This Manual
This service manual has been written and published
by the service department of Mercury Marine to aid
ourdealers’mechanics and companyserviceperson-
nelwhenservicingtheproductsdescribedherein.
It is assumed that these personnel are familiar with
the servicing procedures of these products, or like or
similar products manufactured and marketed by Mer-
curyMarine,thattheyhavebeentrainedintherecom-
mended servicing procedures of these products
which includes the use of mechanic’s common hand
tools and the special Mercury Marine or recom-
mendedtoolsfromothersuppliers.
We could not possibly know of and advise the service
trade of all conceivable procedures by which a ser-
vice might be performed and of the possible hazards
and/or results of each method. We have not under-
taken any such wide evaluation. Therefore, anyone
who uses a service procedure and/or tool, which is
not recommended by the manufacturer, first must
completely satisfy himself that neither his nor the
product’s safety will be endangered by the service
procedureselected.
All information, illustrations and specifications con-
tained in this manual are based on the latest product
information available at the time of publication. As re-
quired,revisions to this manual will be sent to all deal-
ers contracted by us to sell and/or service these prod-
ucts.
It should be kept in mind, while working on the
product,thattheelectricalsystem and ignition system
is capable of violent and damaging short circuits or
severe electrical shocks. When performing any work
where electrical terminals could possibly be
grounded or touched by the mechanic, the battery
cablesshouldbedisconnectedatthebattery.
Any time the intake or exhaust openings are exposed
during service they should be covered to protect
against accidental entrance of foreign material which
could enter the cylinders and cause extensive inter-
nal damage when the engine is started.
It is important to note that, during any maintenance
procedure, replacement fasteners must have the
same measurements and strength as those re-
moved,whethermetric orcustomary.Numberson the
heads of the metric bolts and on surfaces of metric
nuts indicate their strength. Customary bolts use ra-
dial lines for this purpose, while most customary nuts
do not have strength markings. Mismatched or incor-
rect fasteners can result in damage or malfunction, or
possible personal injury. Therefore, fasteners re-
moved should be saved for re-use in the same loca-
tions whenever possible. Where the fasteners are not
satisfactory for re-use care should be taken to select
a replacement that matches the original.

Cleanliness and Care of
Outboard Motor
Amarine powerproductis acombinationof manyma-
chined, honed, polished and lapped surfaces with tol-
erances that are measured in the ten thousands of an
inch. When any product component is serviced, care
and cleanliness are important. Throughout this
manual, it should be understood that proper cleaning,
and protection of machined surfaces and friction
areas is a part of the repair procedure. This is consid-
ered standard shop practice even if not specifically
stated.
Whenever components are removed for service, they
should be retained in order. At the time of installation,
they should be installed in the same locations and
with the same mating surfaces as when removed.
Before raising or removing an outboard engine from a
boat,thefollowingprecautionsshouldbeadheredto:
1. Check that flywheel is secured to end of
crankshaft with a locknut and lifting eye is
threaded into flywheel a minimum of 5 turns.
2. Connect a hoist of suitable strength to the lifting
eye.
In addition, personnel should not work on or under an
engine which is suspended. Engines should be at-
tached to work stands, or lowered to ground as soon
as possible.
We reserve the right to make changes to this manual
without prior notification.
Refer to dealer service bulletins for other pertinent in-
formation concerning the products described in this
manual.
Service Manual Outline
1 - General Information and Specifications
2 - Electrical and Ignition
A - Ignition System
B - Battery, Charging System and
Starting System
C - Timing/Synchronizing and Adjusting
D - Wiring Diagrams
3 A - Fuel System and Carburetion
B - Oil Injection System
4 A - Powerhead (3-Cylinder Engines)
B - Powerhead (4-Cylinder Engines)
5 - Lower Unit
A - Gear Housing
B - Mid Section
C - Shock Absorber
6 - Power Trim
A - Design I (Side Fill Reservoir)
B - Design II (Aft Fill Reservoir)
C - Single Ram
7 - Outboard Motor Installation/Attachments
A - Engine Attachments/Engine Installation
B - Tiller Handle and Co-Pilot

GENERAL INFORMATION
AND SPECIFICATIONS 1

90-13645-2 495
Table Of Contents Page Page
General Specification 1-1. . . . . . . . . . . . . . . . . . . . . .
Cowl Removal 1-3. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Filling Oil Injection System 1-3. . . . . . . . . . . . . . . . . .
Power Trim General Information 1-4. . . . . . . . . . . . .
Trim “In” Angle Adjustment 1-4. . . . . . . . . . . . . . . . .
Models with Power Trim 1-4. . . . . . . . . . . . . . . .
Checking Trim System Fluid Level 1-5. . . . . . . . . . .
Tilt Angle Adjustment 1-5. . . . . . . . . . . . . . . . . . . . . .
Models without Power Trim 1-5. . . . . . . . . . . . . .
Connecting Engine Wiring Harness and
Routing of Engine Battery Cables 1-6. . . . . . . .
Ride-Guide Steering Cable and
Pivot Points Lubrication 1-7. . . . . . . . . . . . . . . . .
Following Complete Submersion 1-8. . . . . . . . . . . .
Salt Water Submersion
(Special Instructions) 1-8. . . . . . . . . . . . . . . .
Submerged While Running
(Special Instructions) 1-8. . . . . . . . . . . . . . . .
Submerged Engine (Fresh Water)
(Plus Special Instructions) 1-8. . . . . . . . . . .
Out-of-Season Outboard Storage 1-9. . . . . . . . . . .
How Weather Affects Engine Performance 1-10. .
Conditions Affecting Operation 1-11. . . . . . . . . . . . .
Detonation: Causes and Prevention 1-12. . . . . . . .
Compression Check 1-12. . . . . . . . . . . . . . . . . . . . . .

1-190-13645--2 1095 GENERAL INFORMATION AND SPECIFICATIONS
General Specification
NOTE: Other specification (torques, etc.) are listed in
the respective sections.
Model 70 Model 75 Model 80 Model 90
Horsepower 70 (52.2 kw) 75 (55.9 kw) 80 (59.6 kw) 90 (67.1 kw)
Idle RPM (in forward gear) 650 - 700
Full Throttle RPM Range 4750 - 5250 5000 - 5500
Piston Replacement 71.12 (1165.7cc)
Cylinder Bore 3.375 (85.7mm)
Stroke 2.65 (67.3mm)
Engine Type 3 Cylinder, 2 Cycle
Ignition Type C.D. Breakerless
Recommended Spark Plug NGK-BUHW-2 or AC-V40 FFK or
Champion L78V Inductor Plugs: NGK-BUZHW-2 or Champion QL78V
Cylinder Firing Order 1-3-2
Recommended Power Trim Fluid Quicksilver Power Trim & Steering Fluid or Automotive Transmission
Fluid (ATF) Type F, FA or Dexron II
Recommended Gasoline Regular Leaded, Premium, Low-Lead and Lead-Free automotive gaso-
lines with a minimum pump posted octane rating of 86
Recommended Oil Quicksilver TC-WII or TC-W3 2-Cycle Outboard Oil
Engine Weight ELO
ELOPT 260 lbs. 280 lbs.
Fuel Tank Capacity 6.6 U.S. Gallons
(5 Imp. Gals.; 25 Liters)
Gear Housing Lubricant Capacity 22.5 fl. oz. (665.3ml)
Gasoline/Oil Ratio at Idle 80:1
Gasoline/Oil Ratio at W.O.T. 50:1
Gear Ratio 2.3:1
Oil Injection Tank Capacity
Tank Capacity 1 gal. (3.78 liter)
Maximum operation per tank
full of oil at W.O.T. 6 hours
Oil remaining when warning
buzzer sounds 1 qt. (.95 liter)
Operating time remaining at
wide open throttle when warn-
ing buzzer sounds 1 Hour

1-2 90-13645--2 1095GENERAL INFORMATION AND SPECIFICATIONS
General Specification
(continued)
NOTE: Other specification (torques, etc.) are listed in
the respective sections.
Model 100 Model 115
Horsepower 100 (74.6 kw) 115 (85.8 kw)
Idle RPM (in forward gear) 650 - 700
Full Throttle RPM Range 4750 - 5250
Piston Replacement 105 (1720.9cc)
Cylinder Bore 3.375 (85.7mm)
Stroke 2.930 (74.4mm)
Engine Type 4 Cylinder, 2 Cycle
Ignition Type C.D. Breakerless
Recommended Spark Plug NGK-BPH8H-N-10* Gap - 0.040 in. (1.0mm)
Inductor Plug NGK BPZ 8H-N-10* Gap - 0.040 in. (1.0mm)
NGK-BUHW
Cylinder Firing Order 1-3-2-4
Recommended Power Trim Fluid Quicksilver Power Trim & Steering Fluid or Automotive Transmission
Fluid (ATF) Type F, FA or Dexron II
Recommended Gasoline Regular Leaded, Premium, Low-Lead and Lead-Free automotive gaso-
lines with a minimum pump posted octane rating of 86
Recommended Oil Quicksilver 2-Cycle Outboard Oil
Engine Weight ELO
ELOPT 340 lbs. 360 lbs.
Fuel Tank Capacity 6.6 U.S. Gallons
(5 Imp. Gals.; 25 Liters)
Gear Housing Lubricant Capacity 22.5 fl. oz. (665.2ml)
Gasoline/Oil Ratio at Idle 80:1
Gasoline/Oil Ratio at W.O.T. 50:1
Gear Ratio 2.07:1
Oil Injection Tank Capacity
Tank Capacity 1.4 gal. (5.3 liters)
Maximum operation per tank
full of oil at W.O.T. 5 hours
Oil remaining when warning
buzzer sounds 1 qt. (.95 liter)
Operating time remaining at
wide open throttle when warn-
ing buzzer sounds 50 min. approx.
*Improves running quality between 1800 – 2000 RPM.

90-13645--2 495 1-3GENERAL INFORMATION AND SPECIFICATIONS
Cowl Removal
Pull outward on starboard side of front shield (a).
Remove spring (b) from latch and open cowls.
18291
a
18292
b
Filling Oil Injection System
Open starboard cowl (refer to cowl removal on this
page).Someearlieroutboardswillhaveacowlbrack-
et to hold cowl open as shown.
Fill tank with recommended oil.
a
a - Oil Tank Tube

1-4 90-13645--2 495GENERAL INFORMATION AND SPECIFICATIONS
Power Trim System
GENERAL INFORMATION
The power trim system is filled at the manufacturer
and is ready for use.
Trim outboard through entire trailering range several
times to remove any air from the system.
The trim system is pressurized and is not externally
vented.Theoutboard canberaised orloweredmanu-
ally by loosening the manual release valve four turns.
The trim “out” angle of this outboard is not adjustable.
The trim system has an internal valve which will
automaticallystop theoutwardtrimtravel at20when
engine RPM is approximately 2000 RPM or higher;
outboard also has to be in water and in gear.
The outboard can be operated beyond the 20trim
limit for operating outboard in shallow water if engine
RPM is kept below approximately 2000 RPM.
a
b
23321
a - Fill Screw (System is Pressurized, DO NOT Open Unless
Outboard is Tilted to Full Up Position)
b - Manual Release Valve
Trim “In” Angle Adjustment
MODELS WITH POWER TRIM
WARNING
Operating some boats with outboard trimmed to the
full “in” trim angle [not using trim adjustment bolt
(a)] at planing speed will cause undesirable and/or
unsafe steering conditions. Each boat MUST BE
water tested for handling characteristics after
outboard installation and after any trim adjust-
ments.
IMPORTANT: Some boat/motor combinations,
thatdonot usethetrimadjustment bolt(a)andare
trimmed to the full “in” trim angle, will not experi-
ence any undesirable and/or unsafe steering
conditions during planing speed. Thus, not using
trim adjustment bolt may be desired. However,
some boats with outboard trimmed to the full “in”
trim angle at planing speeds will cause undesir-
able and/or unsafe steering conditions. If these
steering conditions are experienced, under no
circumstances should the outboard be operated
without the trim adjustment bolt and without the
bolt adjusted in the proper holes to prevent un-
safe handling characteristics.
Water test the boat not using the trim adjustment bolt.
If undesirable and/or unsafe steering conditions are
experienced (boat runs with nose down), install trim
adjustment bolt in proper hole to prevent unsafe han-
dling characteristics.
22744
a

90-13645--2 495 1-5GENERAL INFORMATION AND SPECIFICATIONS
Checking Trim System Fluid Level
IMPORTANT: This trim system is pressurized.
Remove fill screw (b) when outboard is trimmed
to the full “up” position. Retighten fill screw
securely.
1. Trim outboard to full “up” position. Engage tilt lock
lever. Trim systemfluidcanonlybe checkedwhen
outboard is in this position.
2. Removefillscrewand check fluid level. Fluidlevel
should be visible in fill tube.
3. If necessary, add Quicksilver Power Trim and
Steering Fluid; or Automatic Transmission Fluid
(ATF) Type F, FA or Dextron II.
20319
a
b
a - Tilt Lock Lever
b - Fill Screw
Tilt Angle Adjustment
MODELS WITHOUT POWER TRIM
WARNING
Operating some boats at minimum trim “In” at
planing speeds will cause undesirable and/or
unsafe steering conditions. Each boat should be
tested for handling characteristics after any
adjustment is made to the tilt angle.
DO NOT OPERATE motor with tilt lock pin removed.
Adjust tilt angle of motor on transom with tilt lock pin
sothatanti-ventilation plate isaboutparallel and even
with bottom of boat. Speed sometimes may be im-
provedbytiltingmotoroutonetiltpinholetoraise bow
and reduce wetted surface. If motor is tilted in, boat
willridebowdown,wetting more of the bottom andre-
ducing speed, which generally will improve operation
in rough water. Under ideal conditions, efficiency is
best with lower unit operating in level position. Opera-
tion with excessive tilt angle will reduce performance
noticeably and may induce ventilation. It is preferable
to level boat by proper loading rather than by extreme
adjustment of tilt angle.
22744
a
a - Tilt Lock Pin

1-6 90-13645--2 495GENERAL INFORMATION AND SPECIFICATIONS
Connecting Engine Wiring
Harness and Routing of
Engine Battery Cables
WARNING
Cables passing through cowl must be protected
from chafing or being cut, by using the neoprene
sheet as described in the following steps. Failure
to protect cables as described could result in
electrical system failure and/or possible injury to
occupants of boat.
a
b
c
a
b
c
Models with Power Trim
Models without Power Trim
a - Wiring Harness
b - Neoprene Sheet
c - Sta-Straps
1. Plug remote control harness connector into en-
gine harness connector, then secure connector in
place with retainer as shown.
2. Wrap neoprene sheet around cable bundle and
secure each end with a sta-strap. Secure to
bracket with retainer.
IMPORTANT: On Models without Power Trim, the
neoprene sheet must be folded once and then
wrapped around cables as shown.
20290
e
a
b
c
d
f
f
a - Engine Connector
b - Retainer
c - Harness Connector
d - Harness Retainer
e - Neoprene Sheet
f - Sta-Strap(s)
Models with Power Trim

1-790-13645--2 495 GENERAL INFORMATION AND SPECIFICATIONS
Lubrication Points
No. Description Lubricant Used or
Maintenance Fresh Water Frequency Salt Water Frequency
1 Ride-Guide
Steering Cable
2 Throttle-Shift
Linkage Quicksilver
C
E60D
E30D
3Upper Shift Shaft 2-4-C
w/Teflon
Every 60 Days Every 30 Days
4Tilt Tube w
/T
e
fl
on
5Swivel Pin
6Tilt Lock Lever
7Propeller Shaft Quicksilver
-2-4-C w/Teflon
Anti-Corrosion Grease Once in Season Every 60 Days
8Gear Housing Quicksilver Gear Lube Check and fill after 1st 10 days, then every 30 days
Drain and Refill after 1st 25 hours, then after every
100 hours, or once a year before storing.
9Steering Link Rod
Pivot Points SAE 30W Engine Oil Every 60 Days Every 30 Days
10 Power Trim Pump
Oil Level Quicksilver Power Trim and Steering Fluid Every 100 hours, or once in season Same as Fresh Water
--- Engine Crankshaft
Splines to Drive
Shaft Splines
Quicksilver
2-4-C w/Teflon Once in Season by Dealer
11 Accelerator Pump
Stem/Throttle Cam Quicksilver 2-4-C w/Teflon Once in Season Every 60 Days
27868
7
8
20319
6
10
5
Ride-Guide Steering Cable and Pivot
Points Lubrication
WARNING
Core of steering cable (transom end) must be fully
retracted into cable housing before lubricating
cable. If cable is lubricated while extended,
hydraulic lock of cable could occur.
With core of Ride-Guide Steering cable (transom
end) fully retracted, lubricate transom end of steering
cable thru grease fitting and exposed portion of cable
end with Quicksilver 2-4-C w/Teflon. Lubricate all piv-
ot points with SAE 30W engine oil.
50099
1
49

1-8 90-13645--2 495GENERAL INFORMATION AND SPECIFICATIONS
NOTE: 4 CYL. MODELS
22509B
11
11 – LubricationPointsforAccelerator Pump Cam on4Cylinder
Models Only
18298
2
2 – Lubrication Points are indicated with Arrows
Following Complete Submersion
Submerged engine treatment is divided into 3 distinct
problem areas. The most critical is submersion in salt
water; the second is submersion while running.
Salt Water Submersion (Special
Instructions)
Duetothe corrosive effectof saltwateroninternal en-
gine components, complete disassembly is neces-
sary before any attempt is made to start the engine.
Submerged While Running (Special
Instructions)
When an engine is submerged while running, the
possibility of internal engine damage is greatly in-
creased. If, after engine is recovered and with spark
plugs removed, engine fails to turn over freely when
turning flywheel, the possibility of internal damage
(bent connecting rod and/or bent crankshaft) exists.
If this is the case, the powerhead must be disas-
sembled.
Submerged Engine (Fresh Water)
(Plus Special Instructions)
1. Recover engine as quickly as possible.
2. Remove cowling.
3. Flush outside of engine with fresh water to re-
move mud, weeds, etc. DO NOT attempt to start
engine if sand has entered powerhead, as power-
head will be severely damaged. Disassemble
powerhead if necessary to clean components.
4. Remove spark plugs and get as much water as
possible out of powerhead. Most water can be
eliminated by placing engine in a horizontal posi-
tion (with spark plug holes down) and rotating fly-
wheel.
5. Pour alcohol into carburetor throat (alcohol will
absorb water). Again rotate flywheel.
6. Turn engine over and pour alcohol into spark plug
openings and again rotate flywheel.
7. Turn engine over (place spark plug opening
down) and pour engine oil into throat of carbure-
tors while rotating flywheel to distribute oil
throughout crankcase.
8. Again turn engine over and pour approximately
one teaspoon of engine oil into each spark plug
opening. Again rotate flywheel to distribute oil in
cylinders.
9. Remove and clean carburetors and fuel pump
assembly.

1-990-13645--2 495 GENERAL INFORMATION AND SPECIFICATIONS
10. Reinstall spark plugs, carburetors and fuel pump.
11. Attempt to start engine, using a fresh fuel source.
If engine starts, it should be run for at least one
hour to eliminate any water in engine.
12. If engine fails to start, determine cause (fuel, elec-
trical or mechanical). DO NOT allow engine to re-
main idle for more than 2 hours, as serious inter-
nal damage will occur. If unable to start engine in
this period, disassemble engine and clean all
parts and apply oil as soon as possible.
Out-of-Season Outboard Storage
WARNING
As a safety precaution, when boat is in storage,
remove positive (+) battery cable. This will
eliminate possibility of accidental starting of
engine and resultant overheating and damage to
engine from lack of water.
In preparing an outboard for out-of-season storage,
2 precautions must be considered: 1) The engine
must be protected from physical damage and 2) the
engine must be protected from rust, corrosion and
dirt.
1. Remove cowling from engine.
2. Place outboard in water or install Quicksilver
Flushing Attachment over water intake by follow-
ing instructions outlined in “Flushing Cooling Sys-
tem” (see “Table of Contents”).
3. Start engine and allow to warm up. Disconnect
fuel line. When engine starts to stall quickly spray
Quicksilver Storage Seal into each carburetor
throat. Continue to spray until engine dies from
lack of fuel.
4. Remove spark plugs and inject a 5 second spray
of Quicksilver Storage Seal around the inside of
each cylinder. Manually turn engine over several
times to distribute Storage Seal throughout cylin-
ders. Reinstall spark plugs.
5. If engine fuel filter appears to be contaminated, re-
move and replace. Refer to Section 3 “Fuel System
and Carburetion.”
6. Drain and refill lower unit with Quicksilver Gear
Lube, as explained in “Gear Housing Lubrication”
(see “Table of Contents”).
7. Clean outboard thoroughly, including all accessi-
ble powerhead parts, and spray with Corrosion
and Rust Preventive.
8. Refer to lubrication chart in this section (see
“Table of Contents”) and lubricate all lubrication
points.
9. Remove propeller. Apply Quicksilver Anti-Corrosion
Grease or 2-4-C w/Teflon to propeller shaft and re-
install propeller. Refer to “Propeller Installation” (see
“Table of Contents”).
10. If the water pickup is clogged, the speedometer
will be inoperative. Clean the pickup with a piece
of wire or blow out with compressed air. Before
blowing out with air, disconnect the tubing from
the speedometer.
11. To prevent freeze damage, drain the speedome-
ter system of water completely before storage.
Remove tubing from speedometer fitting and
blow thru the tubing to remove water.
12. Store battery as outlined in “Out-of-Season Bat-
tery Storage,” following.
13. For out-of-season storage information on
Autoblend units, refer to Section 8 in this service
manual.
IMPORTANT: When storing outboard for the win-
ter, be sure that all water drain holes in gear hous-
ing are open and free so that all water will drain
out. If a speedometer is installed in the boat, dis-
connect the pickup tube and allow it to drain. Re-
connect the tube after draining. Trapped water
may freeze and expand, thus cracking gear hous-
ing and/or water pump housing. Check and refill
gear housing with Quicksilver Gear Lube before
storage to protect against possible water leakage
into gear housing which is caused by loose lubri-
cant vent plug or loose grease fill plug. Inspect
gaskets under lubricant vent and fill plugs, re-
placing any damaged gaskets, before reinstalling
plugs.

1-10 90-13645--2 495GENERAL INFORMATION AND SPECIFICATIONS
Out-of-Season Battery Storage
1. Remove battery as soon as possible and remove
all grease, sulfate and dirt from top surface.
2. Cover PLATES with distilled water, but not over
3/16 in. (5mm) above perforated baffles.
3. Cover terminal bolts well with grease.
4. Store battery in a COOL, DRY place in a dry car-
ton or box.
5. Remove battery from storage every 60 days.
Check water level and place on charge for 5 to 6
hours at 6 amperes. DO NOT fast charge.
Adischarged battery canbe damagedby freezing.
CAUTION
How Weather Affects Engine
Performance
It is a known fact that weather conditions exert a pro-
found effect on power output of internal combustion
engines. Therefore, established horsepower ratings
refer to the power that the engine will produce at its
rated RPM under a specific combination of weather
conditions.
Corporations internationally have settled on adoption
of I.S.O. (International Standards Organization)
engine test standards, as set forth in I.S.O. 3046
standardizing the computation of horsepower from
data obtained on the dynamometer, correcting all
values to the power that the engine will produce at
sea level, at 30% relative humidity at 77F (25C)
temperature and a barometric pressure of 29.61
inches of mercury.
Summer Conditions of high temperature, low baro-
metric pressure and high humidity all combine to re-
ducetheengine power. This,inturn,is reflectedinde-
creased boat speeds--as much as 2 or 3 miles-per-
hour (3 or 5 Km per-hour) in some cases. (Refer to
previous chart.) Nothing will regain this speed for the
boater, but the coming of cool, dry weather.
In pointing out the practical consequences of weather
effects, an engine--running on a hot, humid summer
day--may encounter a loss of as much as 14% of the
horsepower it would produce on a dry, brisk spring or
fall day. The horsepower, that any internal combus-
tion engine produces, depends upon the density of
the air that it consumes and, in turn, this density is de-
pendent upon the temperature of the air, its baromet-
ric pressure and water vapor (or humidity) content.
Accompanying this weather-inspired loss of power is
a second but more subtle loss. At rigging time in early
spring, the engine was equipped with a propeller that
allowed the engine to turn within its recommended
RPMrangeatfull throttle.With thecomingofthesum-
mer weather and the consequent drop in available
horsepower, this propeller will, in effect, become too
large. Consequently, the engine operates at less than
its recommended RPM.
Due to the horsepower/RPM characteristics of an en-
gine,thiswillresult infurther lossofhorsepoweratthe
propeller with another decrease in boat speed. This
secondary loss, however, can be regained by switch-
ing to a smaller pitch propeller that allows the engine
to again run at recommended RPM.

1-1190-13645--2 495 GENERAL INFORMATION AND SPECIFICATIONS
For boaters to realize optimum engine performance
underchangingweatherconditions, it is essential that
the engine have the proper propeller to allow it to op-
erateatornear thetop endoftherecommendedmax-
imum RPM range at wide-open-throttle with a normal
boat load.
Not only does this allow the engine to develop full
power, butequallyimportant isthefactthatthe engine
also will be operating in an RPM range that discour-
ages damaging detonation. This, of course, en-
hances overall reliability and durability of the engine.
Conditions Affecting Operation
1. Proper positioning of the weight inside the boat
(persons and gear) has a significant effect on the
boat’s performance, for example:
a. Shifting weight to the rear (stern)
(1.) Generally increases top speed.
(2.) If in excess, can cause the boat to por-
poise.
(3.) Can make the bow bounce excessively in
choppy water.
(4.) Will increase the danger of the following -
wave splashing into the boat when coming
off plane.
b. Shifting weight to the front (bow)
(1.) Improves ease of planing off.
(2.) Generally improves rough water ride.
(3.) If excessive, can make the boat veer left
and right (bow steer).
2. Boat Bottom: For maximum speed, a boat bot-
tomshouldbenearlyaflat plane where it contacts
the water and particularly straight and smooth in
fore-and-aft direction.
a. Hook: Exists when bottom is concave in fore-
and-aft direction when viewed from the side.
When boat is planing, “hook” causes more lift
on bottom near transom and allows bow to
drop, thus greatly increasing wetted surface
and reducing boat speed. “Hook” frequently is
caused by supporting boat too far ahead of
transom while hauling on atrailer or during stor-
age.
b. Rocker: The reverse of hook and much less
common. “Rocker” exists if bottom is convex in
fore-and-aft direction when viewed from the
side, and boat has strong tendency to porpoise.
c. Surface Roughness: Moss, barnacles, etc.,
on boat or corrosion of outboard’s gear housing
increase skin friction and cause speed loss.
Clean surfaces when necessary.
3. Gear Housing: If unit is left in the water, marine
vegetation may accumulate over a period of time
in certain types of water. This growth must be re-
moved from unit before operation, as it may clog
the water inlet holes in the gear housing and
cause the engine to overheat.

1-12 90-13645--2495GENERALINFORMATION AND SPECIFICATIONS
Detonation: Causes and Prevention
Detonation in a 2-cycle engine somewhat resembles
the “pinging” heard in an automobile engine. It can be
otherwise described as a tin-like “rattling” or “plinking”
sound.
Detonation generally is thought of as spontaneous ig-
nition, but it is best described as a noisy explosion in
an unburned portion of the fuel/air charge after the
spark plug has fired. Detonation creates severe, un-
timely, shock waves in the engine, and these shock
waves often find or create a weakness: The dome of
a piston, piston rings or piston ring lands, piston pin
and roller bearings.
While there are many causes for detonation in a
2-cycle engine, emphasis is placed on those causes
which are most common in marine 2-cycle applica-
tion. A few, which are not commonly understood, are:
1.Over-advanced ignition timing.
2.Use of low octane gasoline.
3.Propeller pitch too high (engine RPM below rec-
ommended maximum range).
4.Lean fuel mixture at or near wide-open-throttle.
5.Spark plugs (heat range too hot – incorrect reach
– cross-firing).
6.Inadequate engine cooling (deteriorated cooling
system).
7.Combustion chamber/piston deposits (result in
higher compression ratio).
Detonation usually can be prevented, provided that
1)theengineis correctlyset upand2)diligentmainte-
nance is applied to combat the detonation causes,
listed, preceding.
51115
Damaged Piston Resulting from Detonation
Compression Check
1.Remove spark plugs.
2.Install compression gauge in spark plug hole.
3.Hold throttle plates at W.O.T.
4.Crank engine thru at least 4 compression strokes
to obtain highest possible reading.
5.Check and record compression of each cylinder.
Variationofmore than15psi (103.5kPa)between
cylinders indicates that lower compression cylin-
der is in some way defective, such as worn or
sticking piston rings and/or scored piston and cyl-
inder.
6.Compression check is important because an en-
gine with low or uneven compression cannot be
tuned successfully to give peak performance. It is
essential, therefore, that improper compression
be corrected before proceeding with an engine
tune-up.
7.Cylinder scoring: If powerhead shows any indica-
tion of overheating, such as discolored or
scorched paint, visually inspect cylinders for scor-
ing or other damage as outlined in Section 4
“Powerhead.”

IGNITION SYSTEM
ELECTRICAL AND
IGNITION
A
2

90-13645--2 1095
Table Of Contents Page Page
Description 2A-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Test Procedures 2A-1. . . . . . . . . . . . . . . . . . . . . . . . . .
Direct Voltage Adapter (DVA) Tests 2A-1. . . . . .
Troubleshooting Tips 2A-1. . . . . . . . . . . . . . .
Test Sequence 2A-2. . . . . . . . . . . . . . . . . . . . . . .
Ignition System Test Chart 2A-3. . . . . . . . . . . . . . . . .
Stator Test 2A-3. . . . . . . . . . . . . . . . . . . . . . . .
9/18/24 Ampere Stators 2A-4. . . . . . . . . . . .
Ignition Coil Test 2A-5. . . . . . . . . . . . . . . . . . .
Trigger Test 2A-5. . . . . . . . . . . . . . . . . . . . . . .
Ignition (Key) Switch Test 2A-5. . . . . . . . . . .
Commander 2000 Key Switch 2A-5. . . . . . .
Commander Key Switch 2A-5. . . . . . . . . . . .
Ignition Components Removal and
Installation 2A-6. . . . . . . . . . . . . . . . . . . . . . . . . . .
Flywheel 2A-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 2A-6. . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 2A-6. . . . . . . . . . . . . . . . . . . . . . . .
Stator 2A-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 2A-7. . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 2A-7. . . . . . . . . . . . . . . . . . . . . . . .
Trigger 2A-8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Removal 2A-8. . . . . . . . . . . . . . . . . . . . . . . . . .
Installation 2A-8. . . . . . . . . . . . . . . . . . . . . . . .
Ignition Coils (3 Cylinder Models) 2A-9. . . . . . .
Ignition Coils (4 Cylinder Models) 2A-9. . . . . . .
Switch Box 2A-10. . . . . . . . . . . . . . . . . . . . . . . . . .

90-13645--2 1095 2A-1ELECTRICAL AND IGNITION
Description
The outboard ignition system is alternator-driven with
distributor-less capacitor discharge. Major compo-
nents of the ignition system are the flywheel, stator,
trigger, switch box, ignition coils and spark plugs.
The stator assembly is mounted stationary below the
flywheel and has 2 capacitor charging coils. The
flywheel is fitted with permanent magnets inside the
outer rim. As the flywheel rotates the permanent
magnets pass the capacitor charging coils. This
causes the capacitor charging coils to produce AC
voltage. The AC voltage then is conducted to the
switch box where it is rectified and stored in a
capacitor.
The trigger assembly (also mounted under the
flywheel) has 3 coils. The flywheel has a second set
of permanent magnets (located around the center
hub). As the flywheel rotates the second set of
magnets pass the trigger coils. This causes the
trigger coils to produce an AC voltage that is
conducted to an electric Silicon Controlled Rectifier
(SCR) in the switch box.
The switch discharges the capacitor voltage into the
ignition coil at the correct time and firing order
sequence.
Capacitor voltage is conducted to the primary side of
theignitioncoil.The ignitioncoil multipliesthisvoltage
high enough to jump the gap at the spark plug.
The preceding sequence occurs once-per-engine-
revolution for each cylinder.
Spark timing is changed (advanced/retarded) by
rotating the trigger assembly which changes each
trigger coil position in relation to the permanent
magnets on the flywheel center hub.
IMPORTANT: If the engine misfires, runs rough or
does not start, the ignition system should be
checked using a Multi-Meter/DVA Tester
(91-99750), or a voltmeter (capable of measuring
400 volts DC, or higher) and Direct Voltage Adap-
tor (91-89045).
Test Procedures
Direct Voltage Adapter (DVA) Tests
WARNING
DANGER - HIGH VOLTAGE/SHOCK HAZARD! Do
not touch ignition components and/or metal test
probes while engine is running and/or being
“cranked.” STAY CLEAR OF SPARK PLUG
LEADS. To assure personal safety, each
individual spark plug lead should be grounded to
engine.
To protect against meter and/or component
damage, observe the following precautions:
400 VDC* test position (or higher) MUST BE
used for all tests.
INSURE the Positive (+) lead/terminal of DVA is
connected to the Positive (+) receptacle of
meter.
DO NOT CHANGE meter selector switch
position while engine is running and/or being
“cranked.”
Switchbox MUST BEGROUNDED during tests.
Running or “cranking” engine with switch box
ungrounded may damage switch box.
CAUTION
* Ifusingameterwithabuilt-inDVA,theDVA/400VDCtestposi-
tion should be used.
NOTE: Test leads are not supplied with the DVA. Use
test leads supplied with meter.
Test procedures and specifications are provided for
checking primary ignition voltage while the engine
is running and/or being “cranked.”
TROUBLESHOOTING TIPS:
1. Intermittent, weak, or no spark output at two
spark plugs usually indicates a bad TRIGGER.
2. Intermittent, weak, or no spark output at all three
spark plugs usually indicates a bad STATOR or
SWITCH BOX.
3. Intermittent, weak, or no spark at any one spark
plug usually indicates a bad SPARK PLUG,
COIL, or SWITCH BOX.