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Motor Basics - What Every Owner Should
Know As A Bare Minumum
has become very evident to me that 75% of outboard owners have,
basically, little to no knowledge of what they're doing when it comes
to motor maintenence or correct operation. This section is
meant to provide significant guidance to those folks who treat their
motors like a car - WRONG! You need to know about this stuff if
you own a lawnmower, snowblower, chainsaw, weed wacker, and most
importantly, an OUTBOARD!
The other 25% of
you, keep up the good work (just make sure you remember where your
education ends...a little knowledge in the wrong hands can be
|All material on this
website, and these sections, is ©Runner Outboards LLC and is
property. You may freely distribute this information as long as
NOT edited, and credit is given to the author.
information provided should never replace common sense or the
recommendations of the OEM. I do not assume responsibility
the use or misuse of this information. The information provided
based on my experience working as a full time mechanic, on hundreds of
motors over time, reading a lot of manuals, education, and consulting
other experienced mechanics along with a number of retired service reps
I am friends with.
I can offer
any advice from
experience, it would be NOT to try and fix your own motor if you don't
have a good understanding of what you're doing. You need to have
the right special tools, reference materials, and most importantly,
UNDERSTANDING of what is wrong and how to properly fix this
issue. Most people do more harm then good if just messing
around blindly. The reason why I can do these repairs is I've
put in thousands of hours reading, fixing, and practicing. I
something new everyday. I have also gone out and acquired the
necessary, CORRECT tools and reference manuals to work on the
motors. These are very
important to promote correct operation of the motor. The idea is
have a reliable motor, not just one that 'kinda runs.'
Index - Click below to Jump to That Section
Basics, What You Need To Know About Motors
A brief history of
OMC (Outboard Motor Corporation)
Evinrude basically made outboard motors on a large scale in the
1908-09 range, got out of the business for a couple of years, than
restarted under the name ELTO (Evinrude Light Twin Outboards) and ran
the company until the mid
he passed away at the age of 57 after his wife passed away a year
before, and his son assumed control of the company. The first
outboards were actually produced in the late 1800's, with very limited
success and application. They were more of novelty then
viewed as a 'must have.' Remember this is the time of horse drawn
carriages and higher priorities then recreational boating. Just
getting food on the table was more important then water skiing.
As time progressed Evinrude
grew and bought out competitors, such as Johnson. In
mid 1950’s recreational boating gained popularity and with it
production of outboards became much more prevalent. By the mid
more than 6 million small outboards had been produced, so these motors
were engineered through thousands of units and were made to be very
Motor Corporation) was the leader in outboard manufacturing for several
decades but lost traction in the 80's and 90's, and were eventually
bought out in the early 2000's by BRP.
Many of the designs conceived in the 50’s were used right up
today. Looking at a motor from 1958
will be very similar as a modern day motor. In the mid-90's there
was a push for 4-stroke motors, which weigh a lot more and generally
powerful. Blocks and components have been refined but at the end
the day the overall operation of the motor is still the same. The
difference between a 30hp 60's motor and
modern day ETEC may seem significant, but the general principles of how
the motor works is the same. Today's motors simply have
more economic fuel and ignition systems (DFI - direct fuel
injection), but are also computerized.
If you take care of your motor, it will last
years. Most of these outboards still work as well as they did when they
were manufactured 50 years ago for a couple of reasons; they are very
simple; less moving parts means fewer things to fail, and they were
made so that the home owner could do basic repairs and maintenance in
In the early days (up to the 40's/50's), owner's manuals would outline
how to actually carry out repairs on your own. Of course, back in
those days, folks were just plain more intelligent because they needed
to be to survive on their own out on the farm, bayou, etc.
Basically in the early 80's motors became more and more idiot-proof,
because people just plain got lazier and lazier, and flat out less
intellegent. If you look at the average intelligence of a U.S.
citizen, we have consistently lost intelligence for the past 5 decades,
and are no longer ranked even in the top 25 countries in the world in
terms of I.Q.
One reason why motors have big cowels (the motor cover/hood), is
apparently people seemed to think that touching a moving flywheel (the
big round metal disc that's spinning bout 5,000 RPM) was OK. Yep
- idiot proof is the term we're looking for. If you look at
motors prior to WW2, most of them had no cover over the flywheel and
you would use a rope to start it. That all went away once lawyers
started convincing people to become sue happy and not take
responsiblity for their own jackass decision making processes.
OMC was also clever manufacturers because most of their motor lines are
interchangable, or families share the same component. So what
they would do is take a 35hp motor and detune it into a 30, 25, even
20hp motor. Saves a lot in production costs when all you do is
swap out fuel system components, rather than the whole motor.
This also makes it quite a bit easier to find common parts and keep a
Evinrude was bought out by BRP in the early
the Evinrude name lives on. The information I provide is
off of manufacturers recommendations and
my own experience working on 1000+ outboards. I don’t claim to
have all the
answers, but if
you follow the things I recommend here it will certainly make the motor
last a lot longer.
of Outboard – Starting Procedure
Shift to neutral
2. Pump the primer bulb until you feel it
‘hard.’ If you have an older motor with a pressure
tank, press the
primer button on the tank until you feel it become
is the same as the primer bulb on a newer hose line. Make
the cap to the tank is on tight with the older pressure
If you don’t, you’ll keep filling the motor with
gas and flood
it. If you run the motor with the cap loose, the motor will
dying out on you because there won’t be any built up pressure
tank to continuously feed the motor.
3. Advance tiller to
4. Pull choke all the way out
5. Quickly pull the manual starter the
full length of the rope or just before you hit the end of it
6. It may take 1-6 pulls, depending on
temperature of the engine, and how long it was since you last used
it. The reason why it may take more pulls is because there
no fuel in the engine chamber yet, and it needs to be pulled in.
7. Once the motor starts, it may stall
immediately. If it stays running, slowly put the choke
The “choke” restricts air supply inside the motor
so there is more fuel
and less air to promote the engine to fire off. Motors work
igniting fuel and creating an explosion to move pistons, which in turns
a propeller, wheels, a blade (i.e. lawn mower), etc. If the
stalls out immediately, you may need to try starting under ½
no choke. Every motor behaves differently based on
8. Once the motor is running, keep it at
for a minute or two so that it warms up, If it runs rough,
‘coughs’ or skips, this is all fairly normal
initially. It should
smooth out and purr like a kitten once it’s warmed
up. If it
still runs rough, it may be necessary to adjust the rich-lean knob
slightly in either direction 1/16 – 1/8th of a
turn. This minor
adjustment changes how much fuel is being delivered to the motor and
greatly affects operation. With experience you will figure
what your motor likes.
If the motor 'bucks' or runs as if it's
'lugging,' this means it is running rich and you should lean out the
mixture slightly. It will probably smoke a lot too (if it is
running smooth but smoking a lot, don't lean out the mixture this may
be the result of extra oil sitting in the motor or separated out in the
fuel system or tank...make sure you slosh the fuel in your tank around
before each usage to mix the gas and oil). If the motor 'coughs'
(sounds like a backfire), then you are running too lean and the motor
is fuel starved. Richen up the mixture slightly to stop this
Right Way To Pull
Start A Motor
If you've ever had a rope break on you, you already know it's a
miserable thing to go through. Well, this really only happens for
a couple of reasons. Either the rope just wore out normally, or
you (or a previous owner) has been pull starting the motor the wrong
Either the rope, the spring, or the pawl broke. Usually it's the
pawl or the spring, and those only really break after 40 years, or
because somebody has been starting the motor the wrong way.
When you pull start the manual starter, you should gather up the
'slack' in the rope until you feel the pawl engage the flywheel.
From here, pull the rope 2-3 feet quickly. If you don't pull it
quickly, you may not even get any spark in the ignition sytem. If
you don't pull the slack out first, you are litterally ramming the
plastic pawl into the metal flywheel, which doesn't take long to ruin
that plastic or just plain break it.
After you pull it, control the rope retracting in, don't just let
go. Letting go pretty much destroys the spring and the rubber
handle. If you see a bunch of rubber marks around the hole where
the rope comes out of, that because somebody has been letting go of the
handle and letting it fly back in uncontrolled. If you have to
pull the motor over a few times before it starts, repeat the directions
I provided to you.
of Outboard – Shifting and Getting Underway
NEVER shift your motor slowly. This ruins the gears in the
unit/gearcase. ALWAYS shift fast, you should hear a
normally, you SHOULD NOT hear a
‘grinding.’ Grinding is BAD.
2. ALWAYS THROTTLE DOWN TO AS SLOW OF AN
POSSIBLE BEFORE SHIFTING. This saves your gearcase from
3. When the motor is in neutral, you will
allowed to throttle up too high (motors newer than mid 60's, earlier
motors may not have this feature). This is a normal safety
of motors to prevent an accident of shifting into a high idle, which
would result in rapid acceleration of the boat and potential injury
and/or death of the operator and passengers. Conversely, you
can’t shift into neutral when going fast for the same
have to throttle back to shift.
4. Try to accelerate gradually.
This is good
for 3 reasons: 1) better fuel economy 2) you should be able to get up
on plane faster instead of plowing the water (depending on your vessel)
and 3) this reduces wear and tear on your gearcase and on your water
5. Remember the best way to maintain a
is to use it at least every few weeks. Letting them sit for
months or even years is the reason why they stop working.
Use a 50:1 or 25:1 fuel to oil mix. You can go to walmart and
2-stroke outboard motor oil in 16ou. bottles. I recommend
the larger gallon jugs to save a few dollars. Buy 1 of the
bottles and 1 of the gallons. The reason for this is you can
the smaller bottle to measure oil amounts for fuel in the future, use
it as a measuring cup. Use the big gallon to fill the small
one. There is a chart on the back of the bottle explaining
mix the various ratios. General rule of thumb; anything
1960 use 25:1. You can probably get away with 50:1, but more
only protects your motor better. NEVER FORGET TO MIX OIL INTO
YOUR FUEL, OTHERWISE THE MOTOR WILL OVERHEAT, SEIZE, & DIE.
Regardless of year, if you have a 3 or 4hp or below motor, use 24:1.
Change your gearcase oil every 50
usage. You can bring it to a local service person to make sure
you don't have water infiltration, which leads to rapid damage.
YOUR GEARCASE OIL AT THE END OF THE YEAR BEFORE IT GETS TO
FREEZING TEMPERATURES. FAILURE TO DO SO CAN RESULT IN THE
GEARCASE SPLITTING, IN WHICH CASE YOUR MOTOR NO LONGER HAS A WORKING
GEARCASE. Do not store your gearcase empty over
winter. Condensation can form inside and still split the
rust may form on the gears and shorten the life of all moving parts.
If your oil has water in it, smells like rotten eggs, is 'burnt' or
very dark, or milky in appearance, these are all signs that you need
new oil and should have the gearcase evaluated by a mechanic via
pressure testing. Your seals are probably on their way out or
have failed. You should not use the motor again until this is
fixed as you will ruin your gearcase internals. If you're
stranded and MUST use the motor, than refill it and get to where you
need. Then get it serviced.
3. Chain your motor to the transom,
tighten it down. Outboards can jump off the back of the
boat. If you don’t chain it down it may sink and
you lose your
4. If the motor is ever submerged, if you can’t
serviced within 2 hours, keep it submerged. No rust will form
long as it’s submerged. Once removed from water,
plugs and pull the manual starter until all water is dispelled from the
spark plug holes. Once you see water stop coming out, spray
fogging oil into the carb mouth non-stop while turning the motor over
until you see it spitting steadily out of the plug holes. The
idea is to expel as much water as possible and drench everything in oil
to reduce the risk of rust and catastrophic damage.
It will be necessary to remove the carburetor, drain
fuel lines, and clean them to prevent rust. The ignition
will also need to be dried and inspected. If the flywheel is
removed rapidly enough most damage can be avoided. Once
everything is dried out and the ignition system is confirmed to be in
working order, start the motor up ASAP. This will
‘clean it out’
and the motor should be OK. Remember rust doesn't form without
4. Always prepare your motor for long-term storage if
it is going to sit for more than a few weeks, regardless of the time of
year. This involves changing the gearcase oil, fogging the
powerhead, draining all fuel, and lubricating common points found in
the operator's manual.
your impeller as water ejection starts
to drop off. Remember it only takes 30 seconds to overheat
motor if it isn’t being cooled. Bring it to a mechanic for
service - and it's probably not a bad idea to switch your thermostat
too while you're at it. Those do fail without warning and can
lead to an overheat condition.
6. Lubricate all moving
articulations with appropriate grease or oil.
If you want to clean your motor, just
down with WD-40 and use a rag to clean off any unwanted grease or
cosmetic oil. If you see the motor getting dry, rusty, put
and or grease on it to prevent further corrosion. Keeping the
motor oiled will only extend it’s life. Coating it with fogging
oil and WD-40 works well too, just keep in mind the oil will allow
other grime to cling to it over time.
How To Avoid
Killing Your Motor
Check water flow from the back of the motor EVERY USE. If you
the water flow becoming weak or stopping, shut the motor off
RUN THE MOTOR WITHOUT IT BEING IN THE WATER, THIS WILL QUICKLY DAMAGE
THE COOLING SYSTEM, EVEN IN JUST 5 SECONDS.
People who run the motor without being in water are fools.
The reason why is you're making the impeller spin without having water
lubrication, which can cause a cascading set of events to destroy the
motor. If you're ever working on a motor, never spin the
counter-clockwise unless your lower unit is off the motor.
impeller will fold over and be ruined or at the very least weakened.
2. Always mix oil in your
motor. It’s better to
put too much oil in then too little. Fuel ratios: 16:1 pre
pre 1960. 50:1 for motors 1960 and forward. Newer
may say 100:1. Disregard this. Johnson/Evinrude
that such a lean oil mix causes premature failure of internal
parts. Most motors
say on them what they need if they are 1980 or newer. Running
motor with too rich of a mix can cause spark plug fouling because
extra unburned fuel/oil mix can cake up on the spark plugs. The
more smoke too.
If you have a motor below 5 hp use a 24:1 mix regardless of age.
These little motors need the extra oil for internal protection.
No matter what manual you read, follow this advice, it is what the
retired service reps recommend! And those guys were the ones
dealers go to when they can't figure out what's wrong - they are the
gurus when it comes to how and why motors work.
Running Motors Dry
Every time I hear someone say they ran their motor for a few
seconds or even a minute, with no water supply to it, I shake my
pretty much tells
me this person has no idea what they're doing. Will the motor
overheat that fast? Doubtfully (if it's only a minute or
less). But guess what happened in 5 seconds? You destroyed
your water pump (the impeller). It may still work despite this,
but you likely melted the fins, or bent them so that operation will be
impaired, the life definitely shortened. Never run an outboard,
even for just a few seconds, without the lower half of the motor
It's basically like taking your windshield wipers on your car, running
them at max speed, on a dry window on a hot summer day. What do
you think happens to those rubber blades? They essentially melt,
and are almost instantly ruined. The water acts like a lubricant
and keeps the water pump working correctly.
Fuel Tanks &
How To Manage Them
Another really common thing I see is folks completely disregarding
safety with the way they approach the usage of portable fuel
tanks. Depending on what you have, either plastic or metal, you
really need to be aware of the simple fact that gasoline likes to
evaporate and expand when exposed to even minor heat. Take a look
at these pictures below of a tank that has inflated after being left in
the sun for just a few minutes, and how the tank is smaller once vented
If possible, keep the tank out of sunlight. In many instances
this is impractical, or you simply don't have a boat that has a 'below
deck' area. If that is your case, the next best thing is to make
sure the vent cap is working on your tank or if it is not working, you
can ***slightly*** loosen the cap. You can tell the cap is
slightly open if you crack it slightly and hear the familiar hiss of
the fuel vapor escaping.
Keep in mind that if you have a fuel line connected, most tanks have an
automatic 1-way vent when the line is on to relieve the tank of
building up pressure. However this could be malfunctioning
too. If your tank has developed a bloated/pressurized situation,
you may see fuel spray out of the end of either tank side connector or
motor side connector when hooking up the fuel line.
I don't know if you've ever been sprayed in the eye with gas (and
2-stroke oil mixed in), but it is a horrible experience. Not only
can you damage your eyes, but it burns like hell and doesn't go away
for awhile even with a constant water rinse. So slowly open up
your cap in a pressurized tank situation. You may also find that
connecting the hose to your motor instantly fills the carb because the
fuel pressure has forced fuel into the motor. If your carb has a
marginal float or needle and seat, it may start flooding out as the
fuel forces its way in, overflowing the bowl.
The final recommendation is please, don't leave the tank sitting in the
boat as you drive down the road. What we have here essentially is
a 6-gallow molotov cocktail should you make a sudden swerve with your
car. 6 gallons of gas being thrown like a grenade is an
explosive. Store the tank in a secured manner. If you have
a car, you may not be able to put it in the cab for obvious reasons, so
your next best option is to make sure it is strapped securely in your
boat. Also don't drive in your car with the fuel line connected
to your motor. You can easily damage the connectors to snap
the hose line if the tank starts flying around.
One of the most common things I see is rodent damage to motors that
have been put up for storage. This can happen just about
anywhere, including sitting on the back of your boat! If you put
the motor away in a barn, shed, even your garage, mice, squirrels,
chipmunks, etc. might turn your outboard into their next
Taj-Mahal. Besides the obvious health risk of opening up a cover
and a seeing mouse nest, those little varmints cause a lot of damage,
in many cases worst than natural exposure to salt water! They
chew on wires and the urine is so acidic it will destroy metal.
If left to nest long enough, they can cause so much corrosion that the
motor can fall apart. If they go into the fuel system it can
cause big damage to the carburetor and manifold.
Here are a few pics of things I see :
The first couple of photos are an extreme case where a motor had
been left in a shed for 3 years. The cowel could not be removed
because the next was so huge, the latch mechanism was jammed
completely. I had to drill out the lever and use a pry bar to
open the motor. I'll let you guess what words came out of my
mouth when I opened the hood. The last couple of pictures are of
some of the damage done to the motor. This outboard was scrapped
out as it was so badly damaged that it was beyond repair.
To help discourage this from happening, you can put laundry softener
sheets in the motor or moth balls. Both annoy rodents, and you
will need to switch these out every 6 months so they can keep doing
their job. Storing the motor indoors usually is superior to
exterior storage. No matter what you think, all these rodents
need is a hole the size of a nickel to get into the motor, and what
better place to be protected from predators than inside the cowel.
You can see below more pictures of damage from rodent activity. The
urine is so caustic that it can melt metal.
Trim Angle, RPMs, and
I have found a few
tricks that seem to work. None are a 100% guarantee to work
forever, but with trial and error, they seem to work relatively
consistently for me.
1. If the motor is stored outside, loosen the cowel (cover) and
leave it ajar so there is a gap between the lower cowel (motor pan) and
hood. This gap seems to make mice not want to nest, because it
allows predators to go after them.
2. Spray the motor down with WD-40 within the engine
compartment. Not only is this general good practice to keep
rubber and electronics from getting too dry (such as the marine sealant
used on outboard electronics), but the odor seems to repel
3. Store the motor away from vegetation, such as shrubs, high
grass, bushes, or the forest/woods. Optimal areas are in a open
driveway or field. Varments don't like to run across open areas
as predators can pick them off. Again, this is a general rule of
thumb. There are plenty of stupid mice out there....
4. If the motor can be stored indoors, this is always the best
place to protect it, but not in sheds or barns. These are safe
havens for varments and they will search out the safest secluded place
to reside inside a shed or barn.
5. Moth balls and laundry softener sheets don't seem to work in
my experience. They lose their potency relatively quick (softener
sheets very quickly when left outside). Plus the moth ball odor
is horrible in your engine.
There are really just 3 ways to destroy a 2-stroke outboard engine. 1)
Don't put oil in the gas, so it runs straight fuel and overheats. 2)
Run the motor out of the water so it can't cool itself down, and
overheats. OR, the little known THIRD reason, and that is making an
So what does 'LUG' mean? Well, it has to do with the operating range of
the engine at full throttle, or Wide Open Throttle (WOT). Most OMC
motors have a top WOT revolution per minute (RPM) between 4500-6000
When the motor is working at full power, you see better fuel economy,
better boat performance, and it operates as it normally should. So what
effects top RPMs? The main factor is the load that the motor must
handle. So for instance, if you have a light boat with 1 passenger, the
motor will certainly not have to work as hard as a boat that has 6
Load can be affected by a numerous amount of factors other than just
ballast IN the vessel. Water conditions (smooth vs rough waves), wind,
hull design, the vessel climbing out of the water vs. being on
plane...these all effect load. Let's not forget the SIZE of the boat vs
the horsepower rating of the motor. Putting the correct size motor on a
vessel, within the manufacturer's recommended motor horsepower range
has a big influence. For instance, a large motor will have to work less
than a smaller outboard pushing the same load. This is common sense.
You have a few things you can do to improve things, most importantly,
the size of the PROPELLER on the motor. A smaller pitch prop bites into
the water less than a larger pitch prop. It's sort of like when you go
swimming; taking 'doggy paddle' arm strokes is much easier than taking
larger circular strokes with an extended arm. You don't have to work so
hard with smaller paddling vs a large stroke.
Prop pitch makes a big, big difference. When your motor isn't able to
keep up with the load of the boat, you can switch to a smaller pitch
prop to improve top end RPM. This may actually increase overall top
speed in many cases, because the motor can turn higher RPMs and stay
within it's working range. Conversely, using too BIG of a prop makest
he motor 'lug,' which leads to blown cylinders, broken piston rings,
and thrown connecting rods, all of which usually result in catastrophic
damage to an engine. This is true for any engine, the principle were
talking about here...doesn't matter if it's a 2-stroke, a 4-stroke, a
carbureted, or a computerized fuel-injected motor....it's VERY
important to be sure your motor can operate in the top end range it is
rated for when at full throttle.
angle also changes load; the reason is as you trim the boat out of the
water, there is less drag, so the motor has to work less. So once a
boat is on plane, trimming the motor up lifts the bow of the boat out
of the water, and you should see a significant increase in top end RPMs.