Motor Basics
- What Every Owner Should
Know As A Bare Minumum

It 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 dangerous!)

All material on this website, and these sections, is ©Runner Outboards LLC and is intellectual property.  You may freely distribute this information as long as it is NOT edited, and credit is given to the author.

Disclaimer: The information provided should never replace common sense or the recommendations of the OEM.  I do not assume responsibility for the use or misuse of this information.  The information provided is 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.
If 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 learn 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 to have a reliable motor, not just one that 'kinda runs.'

Index - Click below to Jump to That Section

Internal Combustion Essentials
The Basics, What You Need To Know About Motors

Cooling System
Gearcase Components
Ignition System
Fuel System
Mechanical Components
Trailer 101

A brief history of OMC (Outboard Motor Corporation)

Ole 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 1930’s, when 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 the  mid 1950’s recreational boating gained popularity and with it the production of outboards became much more prevalent. By the mid 60’s, more than 6 million small outboards had been produced, so these motors were engineered through thousands of units and were made to be very reliable.  OMC (Outboard 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 through 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 aren’t as powerful.  Blocks and components have been refined but at the end of 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 another 40 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 remote areas.

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 motor running.

Evinrude was bought out by BRP in the early 2000’s, but the Evinrude name lives on.  The information I provide is based 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.

Operation of Outboard – Starting Procedure

1.    Shift to neutral
2.    Pump the primer bulb until you feel it become ‘hard.’ If you have an older motor with a pressure tank, press the primer button on the tank until you feel it become ‘hard.’  This is the same as the primer bulb on a newer hose line.  Make sure the cap to the tank is on tight with the older pressure thanks.  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 keep dying out on you because there won’t be any built up pressure in the tank to continuously feed the motor.
3.    Advance tiller to ‘start’ position
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 the 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 may be no fuel in the engine chamber yet, and it needs to be pulled in.
7.    Once the motor starts, it may stall out immediately.  If it stays running, slowly put the choke in.  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 by igniting fuel and creating an explosion to move pistons, which in turns a propeller, wheels, a blade (i.e. lawn mower), etc.  If the motor stalls out immediately, you may need to try starting under ½ choke or no choke.  Every motor behaves differently based on environmental factors.
8.    Once the motor is running, keep it at high idle 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 out 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 symptom.

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 way.

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.

Operation of Outboard – Shifting and Getting Underway

1.    NEVER shift your motor slowly.  This ruins the gears in the lower unit/gearcase.  ALWAYS shift fast, you should hear a ‘clunk’ normally, you SHOULD NOT hear a ‘grinding.’  Grinding is BAD.
2.    ALWAYS THROTTLE DOWN TO AS SLOW OF AN IDLE AS POSSIBLE BEFORE SHIFTING.  This saves your gearcase from unnecessary abuse!
3.    When the motor is in neutral, you will not be allowed to throttle up too high (motors newer than mid 60's, earlier motors may not have this feature).  This is a normal safety feature 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 reason.  You 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 pump (impeller)
5.    Remember the best way to maintain a working motor is to use it at least every few weeks.  Letting them sit for months or even years is the reason why they stop working.

Maintaining Your Motor

1.    Use a 50:1 or 25:1 fuel to oil mix.  You can go to walmart and buy 2-stroke outboard motor oil in 16ou. bottles.  I recommend buying the larger gallon jugs to save a few dollars.  Buy 1 of the small bottles and 1 of the gallons.  The reason for this is you can use 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 how to mix the various ratios.  General rule of thumb; anything before 1960 use 25:1.  You can probably get away with 50:1, but more oil 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.

2.    Change your gearcase oil every 50 hours of usage.  You can bring it to a local service person to make sure you don't have water infiltration, which leads to rapid damage.

ALWAYS CHANGE 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 case, or 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, don’t just 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 motor. 

4.  If the motor is ever submerged, if you can’t get it serviced within 2 hours, keep it submerged.  No rust will form as long as it’s submerged.  Once removed from water, remove spark 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 all fuel lines, and clean them to prevent rust.  The ignition system 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 oxygen.

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.

5.    Change your impeller as water ejection starts to drop off.  Remember it only takes 30 seconds to overheat your 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.

7.    If you want to clean your motor, just spray it 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 WD-40 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

1.    Check water flow from the back of the motor EVERY USE.  If you see the water flow becoming weak or stopping, shut the motor off immediately.  NEVER 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 flywheel counter-clockwise unless your lower unit is off the motor.  The 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 1950.  24:1 pre 1960.  50:1 for motors 1960 and forward.  Newer motors may say 100:1.  Disregard this.  Johnson/Evinrude figured out 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 a 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 motor may have 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 (No Water)

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 head.  That 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 submerged.

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 (picture 2).

tank1 tank 2

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.

Discouraging Rodent Damage

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 :

2 31 7

4 5

 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.

1  2     5  3  4

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 mice/chipmunks/bugs.

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.

Trim Angle, RPMs, and Performance 2/16/21

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 engine 'LUG.'

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 RPMs.

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 passengers.

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's VERY important to be sure your motor can operate in the top end range it is rated for when at full throttle.

Trim 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.

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